Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America RESEARCH ARTICLE Advanced Science Letters Vol. 4, 3464–3469, 2011 Hydrophilic Interfacing for Thermal Micro Assembly of Polymers (HITMAP) Jeyantt S. Sankaran 1 2 , Swati Goyal 3 , Wintana T. Kahsai 2 4 , Uyen H. T. Pham 2 4 , and Samir M. Iqbal 1 2 5 ∗ 1 Department of Electrical Engineering, 2 Nanotechnology Research and Teaching Facility, University of Texas at Arlington, Arlington, TX 76019, USA 3 Life Technologies Corporation, Carlsbad, CA 92008, USA 4 Department of Bioengineering, 5 Joint Graduate Committee of Bioengineering Program, University of Texas at Arlington and University of Texas Southwestern Medical Center at Dallas, University of Texas at Arlington, Arlington, TX 76019, USA This paper presents a simple approach to create microchannels in polydimethylsiloxane (PDMS) using basic hydrophobic–hydrophilic interactions of polymers. During polymerization, low molecular weight hydrophobic chains of PDMS expel hydrophilic moieties. This phenomenon has been used to create microchannels in PDMS. The process is simple, systematic, flexible in design, easy to implement, rapid, inexpensive and does not require lithography. Fabrication of microchannels in PDMS can be carried out using bench-top tools without the aid of any special facilities or equipment. With directed thermal polymerization over the hot plate, the expulsion of hydrophilic materials creates microchannels along the path traveled by particles. The approach is sensitive to the polymer viscosity, temperature profile and the surface chemistry of the particles. This work can have important implications in reducing the cost and time for prototyping polymer based applications in separation science, cell behavior studies, catalytic membranes and hydrogen storage. The membranes are characterized for electrical continuity and charge effects on conductivity. Keywords: Hydrophilic Particles, Hydrophobic Polymers, Membrane Surface Charges, PDMS Membranes. 1. INTRODUCTION Polydimethylsiloxane (PDMS) is an optically clear organosilane polymer commonly used to fabricate microfluidic channels using soft lithography. It has a very low glass transition temperature of -125  C, can withstand a wide temperature range between -100  C to more than 100  C, has a biologically relevant Young’s modulus, and is biologically inert. 1 2 Various methods have been demonstrated to fabricate microfluidic devices with varying channel sizes and multilevel channel structures. 3–10 Soft lithography has proved to be a powerful technique to fabricate channels, where a master is first fabricated using photolithog- raphy and the elastomeric stamp is then made with patterned relief structures. Inexpensive methods using nylon fiber and low energy templates have also been recently reported. 11 12 Simple porous membranes with pore size of 4–6 m are reported using water as porogen and these membranes have been used as pH sensors. 13 On the other hand, commercial membranes are made by bombardment of heavy ions on polymer surface such as polycarbonate and polyethylene terephthalate, called track-etched membranes. 14 ∗ Author to whom correspondence should be addressed. PDMS has been the material of choice for electrical wire insu- lations for decades owing to its hydrophobic nature that is eas- ily regained due to diffusion of low molar mass PDMS to the surfaces. 15 During polymerization the macromolecules are con- nected into polymeric networks that are three-dimensional. The cross-linking reaction increases the molecular weight and the macromolecular network extends to the whole sample and coex- ists with loose branched networks that are not yet part of the network. This is known as the gel-point (GP). The network con- tinues to grow until all remaining molecules are used as part of the one big network. The reactions at GP are crucial in deter- mining the stiffness and viscosity of PDMS. 16 At GP, phase tran- sition of the prepolymer into a rubber-like material occurs. The process has an associated decrease in the entropy of the system which essentially results from the reduced number of configura- tions that molecular sub-units can have after polymerization. 17 18 The configuration that the sub-units can take and the probabil- ity for these sub-units to become a part of a large network are independent of each other. The overall change in free energy can be separated into enthalpy and entropy components. It has been also reported that PDMS immersed particles do not get interca- lated during polymerization. 19 The work presented here gains its 3464 Adv. Sci. Lett. Vol. 4, No. 11/12, 2011 1936-6612/2011/4/3464/006 doi:10.1166/asl.2011.1865