Biomedical subjects

Lichao Gao

Publications and source records attributed to Lichao Gao.

6 recordsLinked to original sources

PubMed2006

A perfectly hydrophobic surface (thetaA/thetaR = 180 degrees /180 degrees).

A perfectly hydrophobic surface with both advancing and receding water contact angles of 180 degrees was prepared using a facile method on a silicon wafer. Phase separation of a toluene-swollen covalently attached methylsilicone results in a nanoscale network structure that is responsible for the superhydrophobicity. A method for testing extreme hydrophobicity was devised to distinguish between surfaces exhibiting contact angles of 180 and 179 degrees .

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PubMed2006

Contact angle hysteresis explained.

A view of contact angle hysteresis from the perspectives of the three-phase contact line and of the kinetics of contact line motion is given. Arguments are made that advancing and receding are discrete events that have different activation energies. That hysteresis can be quantified as an activation energy by the changes in interfacial area is argued. That this is an appropriate way of viewing hysteresis is demonstrated with examples.

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PubMed2006

"Artificial lotus leaf" prepared using a 1945 patent and a commercial textile.

Two polyester textiles, conventional polyester and microfiber polyester fabrics, were hydrophobized using a simple, patented water-repellent silicone coating procedure. Water contact angles on these two surfaces are theta(A)/theta(R) = 151 degrees/140 degrees and theta(A)/theta(R) = 170 degrees/165 degrees, respectively. A smooth surface of this of this coating exhibits theta(A)/theta(R) = 110 degrees/100 degrees. The binary length scale topography (approximately 2 microm/ approximately 50 microm) of the microfiber polyester is responsible for relieving receding contact line pinning and promoting water repellency that is superior to that of the lotus leaf. The recent literature on superhydrophobic surfaces is criticized for neglecting literature of the 1940s.

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PubMed2006

Two-dimensional fluidics based on differential lyophobicity and gravity.

We have prepared planar fluidics devices using binary chemical patterns consisting of hydrophobic "roads" on which water droplets slide easily and more hydrophobic "curbs" that direct droplet motion. Contact angle and contact angle hysteresis both control the motion of liquid droplets on surfaces. The difference between the advancing contact angles of the two regions prevents the liquid from crossing the interface between them. The low hysteresis of the roads allows facile movement. Gravity (slight tilting of samples) forces droplets to move effortlessly in defined pathways even though the difference in contact angles is not large and both regions are hydrophobic.

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PubMed2006

The "lotus effect" explained: two reasons why two length scales of topography are important.

Surfaces containing 4 x 8 x 40 microm staggered rhombus posts were hydrophobized using two methods. One, using a dimethyldichlorosilane reaction in the vapor phase, introduces a smooth modified layer, and the other, a solution reaction using methyltrichlorosilane, imparts a second (nanoscopic) length scale of topography. The smooth modified surface exhibits contact angles of thetaA/thetaR = 176 degrees /156 degrees . Arguments are made that the pinning of the receding contact line by the post tops (with thetaA/thetaR = 104 degrees /103 degrees ) is responsible for the hysteresis. The second level of topography raises the contact angles of the post tops and the macroscopic sample to theta(A)/theta(R) = >176 degrees />176 degrees and eliminates hysteresis. The increase in Laplace pressure due to the increase in the advancing contact angle of the post tops is a second reason that two length scales of topography are important.

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PubMed2004

Formation of spindlelike aggregates and flowerlike arrays of polystyrene-b-poly(acrylic acid) micelles.

In this letter we describe a simple physical method for the ordered aggregation of scattered single spherical polystyrene-b-poly(acrylic acid) (PS-b-PAA) micelles. First, narrow dispersed spindlelike aggregates, about 60 nm in diameter and 1.5 microm in length, are obtained from the aggregation of single spherical PS-b-PAA micelles at 0 degrees C on a glass slide. Then, the yielding spindlelike units can further aggregate into long-ranged, close-packed, flowerlike arrays after a given amount of freeze-thaw cycles. The formation of the interesting arrays is ascribed to the templated aggregation of micelles on the water polycrystal at the freezing point.

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