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PubMed1997

Ischial pressure sore coverage: a rationale for flap selection.

The role of wound debridement and flap coverage in treating pressure sores is clearly established. However, criteria and supportive clinical data for specific flap selection and the sequence of flaps for coverage of the ischium remain ill-defined. From 1979-1995, 114 consecutive patients underwent flap coverage of 139 ischial pressure sores. Preoperative risk factors, prior flap history, defect size, flap success, complication rates, and the length of hospitalization were retrospectively evaluated and compared for 112 flaps in 87 patients. Flap success was defined as a completely healed wound. Average follow-up was 10 months (range: 1 month-9 years). Overall, 83% (93/112) of the flaps healed. In the majority of cases (75%, 84/112), wound debridement and flap reconstruction was achieved in a single stage. However, there were significant differences in the healing rates among the various flaps used. The inferior gluteus maximus island flap and the inferior gluteal thigh flap had the highest success rates, 94% (32/34) and 93% (25/27), respectively, while the V-Y hamstring flap and the tensor fascia lata flap had the poorest healing rates, 58% (7/12) and 50% (6/12), respectively. Flap success was not significantly affected by the age of the patient or the prior number of flaps used and preoperative risk factors were equally distributed across all types of flaps. The overall complication rate was 37% (41/112), most commonly from a slight wound edge dehiscence (n = 16) that healed with local wound care within one month postoperatively. Results of this study show that proper flap selection and the appropriate sequence of flap use significantly improve success rates for ischial pressure sore coverage in both the short- and long-term. Based upon flap reliability (successful healing rates), reusability, and the need to preserve as many future flap options as possible, a rationale for flap selection is presented which can be individualized to any patient.

Adolescent↗
PubMed1999

Media coverage of chronic diseases in the Netherlands.

OBJECTIVE: Little is known about the quantity or quality of information on rheumatic diseases provided by the mass media. The aim of this study was to gain insight into the media coverage of rheumatic diseases compared with other chronic diseases in the Netherlands. MATERIALS AND METHODS: Newspaper articles, magazine articles, and medical television programs that appeared or were broadcast during a 1-year period, and contained information on rheumatic diseases, heart disease, cancer, chronic lung disease, or diabetes mellitus, were selected for content analysis. For each article and program, it was determined whether coverage concentrated on treatment, influence of lifestyle, scientific progress, or disease consequences. It was also determined whether professional experts and patients were featured. RESULTS: Nine hundred seventeen newspaper articles, 304 magazine articles, and 163 medical programs were found. Most dealt with cancer (43%) and heart disease (37%). The amount of media attention given to each of the five disease categories was found to correspond with mortality but not with prevalence. The contents of the articles and programs differed significantly according to disease topic. The main focus in rheumatic diseases was on patients' experiences, as well as regular and alternative medications. In heart disease and cancer, the main focus was on professional medical viewpoints, operations, and mortality, whereas in chronic lung disease and diabetes it was on treatments in the context of regular medications, scientific progress, and incurability. The influence of lifestyle on the disease process was mentioned most often in connection with diabetes, rheumatic disease, and chronic lung disease. CONCLUSIONS: The amount of attention a disease category received from the media depended on its fatality rates and not on its prevalence. Heart disease and cancer were portrayed as being more serious than the more lingering diseases. Surprisingly, the proportion of articles and programs that included the influence of lifestyle in their coverage was lowest for cancer and heart disease. More frequent and more accurate coverage of chronic diseases, especially rheumatic diseases, is needed if their image is to be brought into line with their importance for and impact on the community.

Chronic Disease↗
PubMed2000

The case of Norplant as an example of media coverage over the life of a new health technology.

BACKGROUND: The contraceptive implant Norplant (levonorgestrel) had a fairly short life in the UK. This made it a convenient subject for a case study of how media coverage alters over time. We set out to produce a critical description of national newspaper coverage of Norplant over the course of its use in the UK. METHODS: We searched newspaper databases and press-clippings files for articles about Norplant printed between 1992 and 1996. For those that met our inclusion criteria, we extracted bibliographical data, made a standardised judgment about the "slant" of the article towards Norplant, and used qualitative techniques to analyse the content of the articles. FINDINGS: 101 national newspaper articles were included in the study. Norplant attracted media coverage over the course of its career, but the slant of articles shifted dramatically over time from a favourable to a negative presentation. This reflected the use of different story types over the course of time. Early reports presented Norplant very positively as either a clear improvement on existing contraceptive methods or a valuable addition to the range. Any disadvantages were down-played. The positive image of Norplant was reinforced immediately after its official launch by reports that it was in great demand but women might be denied access to it. Less than a year later, however, newspaper reports about Norplant were dominated by the stories of individual women who had had bad experiences with the product. INTERPRETATION: Three main reporting themes were seen. At first, Norplant was presented as a positive new development, and one that might be denied to people. In later coverage it became a flawed and damaging product. These themes recur in media reporting of health technologies, and the fact that they occur at different stages in a product's career means that a balanced assessment of the technology is not usually feasible from media reporting at any one time. An appreciation of the forms and implications of these reporting frameworks could help health-care providers and users to appraise media reports more critically.

Contraceptive Agents, Female↗
PubMedDate not supplied

Monetary incentives in primary health care and effects on use and coverage of preventive health care interventions in rural Honduras: cluster randomised trial.

BACKGROUND: Scaling-up of effective preventive interventions in child and maternal health is constrained in many developing countries by lack of demand. In Latin America, some governments have been trying to increase demand for health interventions by making direct payments to poor households contingent on them keeping up-to-date with preventive health services. We undertook a public health programme effectiveness trial in Honduras to assess this approach, contrasting it with a direct transfer of resources to local health teams. METHODS: 70 municipalities were selected because they had the country's highest prevalence of malnutrition. They were allocated at random to four groups: money to households; resources to local health teams combined with a community-based nutrition intervention; both packages; and neither. Evaluation surveys of about 5600 households were undertaken at baseline and roughly 2 years later. Pregnant women and mothers of children younger than 3 years old were asked about use of health services (primary outcome) and coverage of interventions such as immunisation and growth monitoring (secondary outcome). Reports were supplemented with data from children's health cards and government service utilisation data. Analysis was by mixed effects regression, accounting for the municipality-level randomisation. FINDINGS: The household-level intervention had a large impact (15-20 percentage points; p<0.01) on the reported coverage of antenatal care and well-child check-ups. Childhood immunisation series could thus be started more opportunely, and the coverage of growth monitoring was markedly increased (15-21 percentage points; p<0.01. Measles and tetanus toxoid immunisation were not affected. The transfer of resources to local health teams could not be implemented properly because of legal complications. INTERPRETATION: Conditional payments to households increase the use and coverage of preventive health care interventions.

Adolescent↗
PubMed2003

Impact of target volume coverage with Radiation Therapy Oncology Group (RTOG) 98-05 guidelines for transrectal ultrasound guided permanent Iodine-125 prostate implants.

PURPOSE: Despite the wide use of permanent prostate implants for the treatment of early stage prostate cancer, there is no consensus for optimal pre-implant planning guidelines that results in maximal post-implant target coverage. The purpose of this study was to compare post-implant target volume coverage and dosimetry between patients treated before and after Radiation Therapy Oncology Group (RTOG) 98-05 guidelines were adopted using several dosimetric endpoints. MATERIALS AND METHODS: Ten consecutively treated patients before the adoption of the RTOG 98-05 planning guidelines were compared with ten consecutively treated patients after implementation of the guidelines. Pre-implant planning for patients treated pre-RTOG was based on the clinical target volume (CTV) defined by the pre-implant TRUS definition of the prostate. The CTV was expanded in each dimension according to RTOG 98-05 and defined as the planning target volume. The evaluation target volume was defined as the post-implant computed tomography definition of the prostate based on RTOG 98-05 protocol recommendations. Implant quality indicators included V(100), V(90), V(100), and Coverage Index (CI). RESULTS: The pre-RTOG median V(100), V(90), D(90), and CI values were 82.8, 88.9%, 126.5 Gy, and 17.1, respectively. The median post-RTOG V(100), V(90), D(90), and CI values were 96.0, 97.8%, 169.2 Gy, and 4.0, respectively. These differences were all statistically significant. CONCLUSIONS: Implementation of the RTOG 98-05 implant planning guidelines has increased coverage of the prostate by the prescription isodose lines compared with our previous technique, as indicated by post-implant dosimetry indices such as V(100), V(90), D(90). The CI was also improved significantly with the protocol guidelines. Our data confirms the validity of the RTOG 98-05 implant guidelines for pre-implant planning as it relates to enlargement of the CTV to ensure adequate margin between the CTV and the prescription isodose lines.

Adult↗
PubMed2004

Universal health coverage in Thailand: ideas for reform and policy struggling.

Inequality in health between rich and poor in Thailand was well documented; millions of informal workers and their families lacked health insurance; and the poor paid more proportionately in income for health care. The universal coverage is conceived as one of the means to redress the situation. But the term 'universal coverage' may mean differently among different groups of stakeholders. This paper, based on empirical research of health policy reform, collected perceptions and ideas from stakeholders and discusses the ways and strategies that universal coverage might take shape in Thailand. Two sources of information were taken: one from the questionnaire survey (according to the Delphi technique, two rounds of survey were taken), another an in-depth interview. Obtained information for policy formulation included how best, as conceived by stakeholders, to implement the universal coverage, sources of finance, fiscal implication for Thai government, ways to prevent higher demand for unnecessary services, and involvement of local government. Recent policy move in Thailand (the so-called 30 baht for all diseases) emerged in 2001 generated hot debate nationwide. The programme is currently in its early phase and is likely to evolve overtime--i.e. whether or not this programme will be financed by certain types of taxes or from annual government expense still unclear; and budget allocation among different health providers still unsettled. Anyhow this programme may be interpreted as a policy shift away from the pro-market based toward a government-supported egalitarianism.

Attitude to Health↗
PubMed2003

The measurement of influenza vaccine coverage among health care workers.

BACKGROUND: Annual influenza vaccination is recommended for health care workers in both the United States and Canada. Estimations of vaccine coverage are commonly used to evaluate these vaccination programs. PURPOSE: We identify, discuss, and illustrate challenges including definitions of health care worker (HCW), selection of indicators, and data sources in the estimation of staff influenza vaccination coverage rates. METHODS: To illustrate the impact of the factors we discuss, we created a database of a simulated pool of HCWs that included varying proportions of permanent, casual, and contract staff under differing scenarios of staff turnover and differing probabilities of individuals being vaccinated. The Excel 97 random number generator (Microsoft) was used to randomly allocate the HCW to different strata under differing staff turnover rates and to designate individuals as being vaccinated. RESULTS: The nature of the staff targeted in the program policy has a large impact on the estimations of vaccine coverage. Different indicators provide data that might be useful for different purposes. The counts in the numerator and denominator of a period prevalence may be useful for estimation of the total workload required of the vaccination program. An incidence density might be useful as an indicator of the efficiency of the program in "capturing" staff for vaccination. The indicator that may be easiest is the point prevalence. CONCLUSION: Program evaluators must think carefully when planning to estimate staff vaccination coverage to avoid invalid comparisons of estimates over time and place. State or province-wide targets for health care worker (HCW) vaccination may be meaningless unless appropriate criteria for the calculation of influenza vaccination rates are developed and specified.

Allied Health Personnel↗
PubMedDate not supplied

[Documented immunization coverage in second-year primary schoolchildren from the province of Valladolid].

OBJECTIVE: To estimate the documented immunization coverage and degree to which schoolchildren's vaccination cards are kept up to date. METHODS: Transversal descriptive study of children in the second year of primary education in the province of Valladolid during the 1999-2000 academic year. The sample consisted of 698 children with a participation rate of 82%. The percentage of children whose immunization schedule was up to date in accordance with their age, that of children with additional vaccinations and the accuracy of the vaccination cards was quantified. Information was collected through a questionnaire on vaccination cards or, for children without one, from their medical history. RESULTS: The documented immunization coverage was 99.3% (95% CI: 98.6-99.9) for the first three dose of diphtheria toxoid, tetanus toxoid and pertussis vaccine and poliomyelitis vaccine, 98.9% (95% CI: 97.7-99.5) for the measles, mumps and rubella vaccine and 95% (95% CI: 93.4-96.7) for all doses up to the age of six. In addition, 7.2% (95% CI: 5.3-9.2) were immunized against hepatitis B, 14.4% (95% CI: 11.6-17) against Haemophilus influenzae type B and 90.3% (95% CI: 88-92.5) against meningococal A + C. A total of 84.4% of vaccination cards were correctly filled in (95% CI: 81.7-87.2). CONCLUSIONS: Systematic immunization coverage in the schoolchildren was high. Because of their accuracy, vaccination cards were a useful tool for determining immunization coverage. Both the accuracy of the vaccination card and the incidence of non-systematic immunization were higher in urban areas.

Child↗
PubMedDate not supplied

[Child vaccination coverage in a rural community: prevalence and related factors].

In the rural environment investigations on vaccination coverage during the daily consultation of Primary Care is feasible. For knowing the real levels and improve the situation, infant vaccination coverage was studied in a rural township with hamlet (small villages) by interviewing the parents and checking the vaccination card. Demographics variables were also analysed looking for different coverage according to these characteristics. One hundred and five children from 0 to 14 years were studied. Relative risks were calculated for the situation of no vaccination. The 69% have got vaccination card. Vaccination rates for Tetanus, Oral Polio, Triple Virus (Measles, Rubella, Mumps) and Rubella (73.3%, 73.3%, 75.5% and 83.3% respectively) were not enough for its eradication. The older children and those who have the biggest family size, showed less rates. Those who live in hamlets have a greater risk to not to be vaccinate, being able to perform "bags" of the deficient vaccination. This survey has allowed to get a complete register of infant vaccination coverage and start correcting actions of the deficiencies noticed.

Adolescent↗
PubMed2003

A population-based register study of vaccine coverage among children in Greenland.

To assess coverage rates of standard childhood vaccinations in Greenland, a geographically isolated and sparsely populated area, and to determine risk factors for low coverage, we performed a register-based cohort study among 596 children from 1993 to 1998 in Sisimiut, Greenland. For vaccines given before the age of 2 years (pertussis 1-3, DT-IPV 1-3, and MMR 1) coverage rates in general were impressively high being on or above levels of Western countries. A risk factor for low coverage was migration. The Greenlandic vaccination model with free vaccinations administered by health workers who systematically call in children at scheduled times seems highly efficient and could be a model for other similar countries.

Child↗
PubMed2001

Distant pedicle flaps for soft tissue coverage of severely burned hands: an old idea revisited.

Burns to the hand that are complicated by exposure of bone, joint or tendon cannot be closed with conventional skin grafts and require flap procedures to prevent further damage. Local or regional flaps may be unavailable if electrical or blast trauma produces a large zone of injury, or when forearm burn injury extends beyond fascia. Free tissue transfer may not be tolerated by critically ill burn patients. In these circumstances, distant pedicle flaps are one option for safe and effective soft tissue coverage. Over a 5-year period, we have performed six distal pedicle flaps for coverage of exposed hand structures when local or free flaps were contraindicated or unavailable. The patients required an average of 4.5 surgical procedures to complete hand reconstruction and soft tissue coverage. Soft tissue coverage was completely successful in five patients and partially successful in one patient. Single stage local or free flaps remain the treatment of choice when burned hands cannot be covered with skin grafts. When these flap options are not available, distant pedicle flaps provide a safe alternative.

Adolescent↗
PubMed1998

Comprehensive irradiation of head and neck cancer using conformal multisegmental fields: assessment of target coverage and noninvolved tissue sparing.

PURPOSE: Conformal treatment using static multisegmental intensity modulation was developed for patients requiring comprehensive irradiation for head and neck cancer. The major aim is sparing major salivary gland function while adequately treating the targets. To assess the adequacy of the conformal plans regarding target coverage and dose homogeneity, they were compared with standard irradiation plans. METHODS AND MATERIALS: Fifteen patients with stage III/IV head and neck cancer requiring comprehensive, bilateral neck irradiation participated in this study. CT-based treatment plans included five to six nonopposed fields, each having two to four in-field segments. Fields and segments were devised using beam's eye views of the planning target volumes (PTVs), noninvolved organs, and isodose surfaces, to achieve homogeneous dose distribution that encompassed the targets and spared major salivary gland tissue. For comparison, standard three-field radiation plans were devised retrospectively for each patient, with the same CT-derived targets used for the clinical (conformal) plans. Saliva flow rates from each major salivary gland were measured before and periodically after treatment. RESULTS: On average, the minimal dose to the primary PTVs in the conformal plans [95.2% of the prescribed dose, standard deviation (SD) 4%] was higher than in the standard plans (91%, SD 7%; p = 0.02), and target volumes receiving <95% or <90% of the prescribed dose were smaller in the conformal plans (p = 0.004 and 0.02, respectively). Similar advantages of the conformal plans compared to standard plans were found in ipsilateral jugular nodes PTV coverage. The reason for underdosing in the standard treatment plans was primarily failure of electron beams to fully encompass targets. No significant differences were found in contralateral jugular or posterior neck nodes coverage. The minimal dose to the retropharyngeal nodes was higher in the standard plans. However, all conformal plans achieved the planning goal of delivering 50 Gy to these nodes. In the conformal plans, the magnitude and volumes of high doses in noninvolved tissue were significantly reduced. The main reasons for hot spots in the standard plans (whose dose calculations included missing tissue compensators) were photon/electron match line inhomogeneities, which were avoided in the conformal plans. The mean doses to all the major salivary glands, notably the contralateral parotid (receiving on average 32% of the prescribed dose, SD 7%) were significantly lower in the conformal plans compared with standard radiation plans. The mean dose to the noninvolved oral cavity tended to be lower in the conformal plans (p = 0.07). One to 3 months after radiation, on average 60% (SD 49%) of the preradiation saliva flow rate was retained in the contralateral parotid glands and 10% (SD 16%) was retained in the submandibular/sublingual glands. CONCLUSIONS: Planning and delivery of comprehensive irradiation for head and neck cancer using static, multisegmental intensity modulation are feasible. Target coverage has not been compromised and dose distributions in noninvolved tissue are favorable compared with standard radiation. Substantial major salivary gland function can be retained.

Carcinoma, Squamous Cell↗
PubMed2003

Frequency and coverage of trinucleotide repeats in eukaryotes.

In the aim to assess whether the tri-repeat shortage reported in vertebrates affects specific motifs, such as those causing neuromuscular diseases in man, we detected approximate di-, tri- and tetra-repeats (STR) longer than 25 bases in human chromosomes 21 and 22, and in some model organisms (M. musculus, D. melanogaster, C. elegans, A. thaliana and S. cerevisiae). We found that overall STR are more represented in mouse and in man than in the other organisms. However, tri-repeats are less represented than di- and tetra- in man and mouse, but show intermediate values between di- and tetra- in the other organisms. In man, ACG shows the lowest both frequency and coverage, ATC the highest coverage and AAT the highest frequency. In general, coverage and frequency of tri-repeats are linearly related, except for ACC, ATC, AAG, AGG motifs in man and AAG, AGG in mouse, which exhibit unexpectedly long repeats. Often their copy numbers exceed that found responsible for the dynamic mutations, set at around 40. The shortage in frequency and coverage of tri- vs. di- and tetra-repeats observed in man and mouse can be ascribed to a subset of the remaining tri-repeat motifs, but among them those recognized as dynamically mutable (AAG, AGC and CCG) are not the least represented. Possible constraints in tri-repeat expansion seem to be structural and conserved along the evolutionary scale: a motif-specific relaxation of the relevant controls may be responsible for the occasional expansions found in mouse and man.

Animals↗
PubMed2001

Comparison of NIS and NHIS/NIPRCS vaccination coverage estimates. National Immunization Survey. National Health Interview Survey/National Immunization Provider Record Check Study.

BACKGROUND: The National Immunization Survey (NIS) and the National Health Interview Survey (NHIS) produce national coverage estimates for children aged 19 months to 35 months. The NIS is a cost-effective, random-digit-dialing telephone survey that produces national and state-level vaccination coverage estimates. The National Immunization Provider Record Check Study (NIPRCS) is conducted in conjunction with the annual NHIS, which is a face-to-face household survey. As the NIS is a telephone survey, potential coverage bias exists as the survey excludes children living in nontelephone households. METHODS: To assess the validity of estimates of vaccine coverage from the NIS, we compared 1995 and 1996 NIS national estimates with results from the NHIS/NIPRCS for the same years. RESULTS: Both the NIS and the NHIS/NIPRCS produce similar results. CONCLUSION: The NHIS/NIPRCS supports the findings of the NIS.

Child, Preschool↗
PubMed2001

Provider characteristics and behaviors as predictors of immunization coverage.

BACKGROUND: Most studies of immunization behaviors measure adherence to standard immunization practices, relying on surveys without linking reported behaviors to objectively measured immunization rates. This study attempts to close that gap. METHODS: In 1997, pediatric, family, and general providers in Pennsylvania serving children aged < 36 months (N = 251) completed immunization behavior surveys. We linked these responses to patient chart audits for practice-level immunization rates. RESULTS: Immunization rates for our sample fell short of national goals (average up-to-date immunization status at 12 months = 69%). They were significantly higher for pediatricians than for family/general practitioners (78% vs 58%, p < 0.001) and for practices treating > or = 100 children in the past 30 working days than for those treating < 100 children (77% vs 62%, p < 0.001). Behaviors with significant associations to higher immunization coverage were: (1) appropriately giving diphtheria, tetanus toxoids, and pertussis immunization under false contraindications versus withholding it (73% vs 66%, p < 0.05); (2) willingness to give at least four injections at one visit versus fewer injections (74% vs 65%, p < 0.01); and (3) holding immunization in-service training versus no training (71% vs 65%, p < 0.05). However, multivariate analysis showed that only provider specialty remained a significant predictor of coverage. CONCLUSIONS: Pediatricians have higher coverage rates than family/general practitioners. Although pediatricians see more children, the number of immunization-delayed children at 12 months is approximately the same for both provider groups. Therefore, efforts to improve coverage should continue to be directed toward both groups.

Child, Preschool↗
PubMed2002

Universal coverage and its impact on reproductive health services in Thailand.

Thailand has recently introduced universal health care coverage for 45 million of its people, financed by general tax revenue. A capitation contract model was adopted to purchase ambulatory and hospital care, and preventive care and promotion, including reproductive health services, from public and private service providers. This paper describes the health financing system prior to universal coverage, and the extent to which Thailand has achieved reproductive health objectives prior to this reform. It then analyses the potential impact of universal coverage on reproductive health services. Whether there are positive or negative effects on reproductive health services will depend on the interaction between three key aspects: awareness of entitlement on the part of intended beneficiaries of services, the response of health care providers to capitation, and the capacity of purchasers to monitor and enforce contracts. In rural areas, the district public health system is the sole service provider and the contractual relationship requires trust and positive engagement with purchasers. We recommend an evidence-based approach to fine-tune the reproductive health services benefits package under universal coverage, as well as improved institutional capacity for purchasers and the active participation of civil society and other partners to empower beneficiaries.

Financing, Government↗
PubMed2002

Influenza and pneumococcal vaccine distribution and use in primary care and hospital settings in Scotland: coverage, practice and policies.

A survey of the coverage, distribution and the factors associated with use of influenza and pneumococcal vaccines among general practitioners (GPs) in primary care and in hospital settings was carried out in 53 general practices in Scotland taking part in the 'Continuous Morbidity Recording' (CMR) programme. The annual vaccine distribution increased substantially among 53 general practices from 1993 to 1999 and in Scotland as a whole from 1984 to 1999. From the questionnaire, overall coverage was 43% (95% CI 38-48) for influenza vaccine in the 2000-1 season and 13% (95% CI 9-16) for pneumococcal vaccine in the last 5 year period, in high-risk patients recommended for these vaccines by the Department of Health (DoH). Influenza vaccine coverage was highest in the elderly (65 years of age and above) at 62% (95% CI 59-74). Although pneumococcal vaccination is not currently recommended for all elderly, coverage of this vaccine was also higher in this group (22%, 95% CI 16-29). In the majority of patients (influenza vaccine, 98% and pneumococcal vaccine, 94%), vaccination was carried out in general practice. Only 2% of patients had received pneumococcal vaccination in a hospital setting. The level of influenza and pneumococcal vaccination varied with the level of deprivation. Most GPs considered that the responsibility for influenza and pneumococcal vaccination lay with them. Forty-five percent of GPs reported having a written policy with set target for influenza vaccination and 11% for pneumococcal vaccination.

Aged↗
PubMed2002

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 1. Effects of temperature, surface coverage, and preparation procedure.

Raman spectroscopy is used to examine the effects of temperature, surface coverage, nature of the alkylsilane precursor (octadecyltrichlorosilane, methyloctadecyldichlorosilane, or dimethyloctadecylchlorosilane), and surface grafting method (surface or solution polymerized) on alkyl chain conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Conformational order is assessed using the intensity ratio of the antisymmetric and symmetric v(CH2) modes as well as the frequency at which these Raman bands are observed. Conformational order increases with surface coverage. Temperature-induced surface phase changes are observed between 258 and 343 K for this homologous series of stationary phases that are demonstrated to adhere to the Clapeyron equation for a simple first-order transition. Phase changes are discussed in terms of variation of the molar enthalpy, molar entropy, and molar volume of the stationary phase, all of which depend on surface coverage. For the limited range of systems investigated, a correlation between stationary-phase preparation (surface versus solution polymerized and nature of the silane precursor) and extent of alkyl chain order is not clearly observed.Instead, akyl chain order is largely dependent on bonding density. A molecular picture of temperature-induced disorder in octadecylsilane stationary phases is proposed, with disorder originating at the distal carbon and propagating toward the proximal carbon.

Molecular Conformation↗