An analytical model for the wettability switching characteristic of a nanostructured thermoresponsive surface

The applications of thermoresponsive surfaces require the development of a rigorous mathematical treatment for these surfaces to understand and improve their behavior. We propose an analytical model to describe the transfer characteristics (variation in contact angle versus temperature) of a unique nanostructured thermosensitive surface, consisting of silica nanoparticles and a hydrophilic/hydrophobic thermoresponsive polymer, poly(N-isopropylacrylamide). Three different thermo-sensitive platforms were fabricated and the contact angle change of a water droplet on the surface with varying surface temperature was analytically modeled

Integration Of A Nanostructure Embedded Thermoresponsive Polymer For Microfluidic Applications

This work describes the modeling, synthesis, integration and characterization of a novel nanostructure embedded thermoresponsive material for microfluidic applications. The innumerable applications of thermoresponsive surfaces in the recent years have necessitated the development of a rigorous mathematical treatment for these surfaces to understand and improve their behavior. An analytical model is proposed to describe the transfer characteristic (variation of contact angle versus temperature) of a unique switchable, nanostructured, thermoresponsive surface consisting of silica nanoparticles and the thermoresponsive polymer, Poly(N-isopropylacrylamide ) (PNIPAAm) which changes its wetting angle upon heating. Important metrics such as the absolute lower critical solution temperature, threshold & saturation temperatures and gain are modeled and quantified by mathematical expressions. Based on the modeling, a heat source for the thermoresponsive surface was integrated on the glass substrate itself to create a fully functional smart surface. The design and fabrication of a smart platform consisting of the switchable, nanostructured, thermoresponsive surface with an integrated gold microheater for wettability control and its time response analysis was conducted. The insight gained into the behavior of the thermoresponsive surface by using the analytical model, aided the effort in the effective integration of the surface into a microfluidic channel for flow regulation applications. The implementations of novel microfluidic flow regulator concepts were tested. The aim is to integrate a regulator function to a channel surface utilizing the layer-by-layer (LBL) deposition technique. The characterization and pressure differential study of the microfluidic regulators was carried out on simple straight microchannels which were selectively coated with the thermoresponsive surface. Theoretical and experimental studies were performed to determine the important characteristic parameters including capillary, Weber and Reynolds numbers. The pressure differential data was used to develop critical operating specifications. This work lays out a new microfluidic device concept consisting of a channel with a built-in regulatory function

IMECE2008-68732 1 A NANOSTRUCTURED THERMOSENSITIVE SMART SURFACE WITH INTEGRATED MICROHEATER FOR WETTABILITY CONTROL

ABSTRACT This paper describes the design and fabrication of a switchable thermosensitive polymer with an integrated microheater as a smart surface platform for wettabilty control. The thermoresponsive surface is synthesized on a glass substrate using the polymer poly(N-isopropylacrylamide) (PNIPAAm) which can change its wettability when subjected to change in temperature. PNIPAAm is hydrophilic when the surface temperature is less than the lower critical solution temperature (LCST) range of about 28-33 ºC and is hydrophobic above the LCST range. The PNIPAAm surface is heated by spiral gold microheaters which are fabricated on the lower side of the glass substrate. The contact angle change with change in temperature is tested using a standard goniometer. Time response analysis of the surface is presented. This smart surface can be used as an active or adaptive component for microflow regulation and can be potentially integrated into large scale lab-on-chip (LOC) systems

A Nanostructured Thermosensitive Smart Surface With Integrated Microheater For Wettability Control

This paper describes the design and fabrication of a switchable thermosensitive polymer with an integrated microheater as a smart surface platform for wettabilty control. The thermoresponsive surface is synthesized on a glass substrate using the polymer poly(N-isopropylacrylamide) (PNIPAAm) which can change its wettability when subjected to change in temperature. PNIPAAm is hydrophilic when the surface temperature is less than the lower critical solution temperature (LCST) range of about 28-33°C and is hydrophobic above the LCST range. The PNIPAAm surface is heated by spiral gold microheaters which are fabricated on the lower side of the glass substrate. The contact angle change with change in temperature is tested using a standard goniometer. Time response analysis of the surface is presented. This smart surface can be used as an active or adaptive component for microflow regulation and can be potentially integrated into large scale lab-on-chip (LOC) systems. Copyright © 2008 by ASME

Wettability Control And Flow Regulation Using A Nanostructure-Embedded Surface

This work addresses the synthesis, integration and characterization of a nanostructure-embedded thermoresponsive surface for flow regulation. In order to create a hierarchic structure which consists of microscale texture and nanoscale sub-texture, hybrid multilayers consisting of poly(allylamine hydrochloride) (PAH), poly(acrylic acid) (PAA) and colloidal silica nanoparticles (average diameter=22 nm and 7 nm) were used. Based on the electrostatic interactions between the polyelectrolytes and nanoparticles, a layer-by-layer deposition technique in combination with photolithography was employed to obtain a localized, conformally-coated patch in a microchannel. Grafted with the thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), wettability of the surface could be tuned upon heating or cooling. The measurement of differential pressure at various stages of device verified the working conditions of the nanostructure-embedded surface for regulating a capillary flow in the microchannel. Copyright © 2011 American Scientific Publishers All rights reserved

Conformal Switchable Superhydrophobic/Hydrophilic Surfaces For Microscale Flow Control

The development of microvalves is essential to realize a fully integrated system for nano/microliter fluid handling in microfluidic devices. Microvalves that utilize passive fluidic manipulation employ a hydrophobic surface in a microchannel network in which the operation is controlled by the interfacial tension of the liquid-air-solid interface. In order to obtain a switchable valve in microfluidic channels, conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated by the layer-by-layer deposition of poly(allylamine hydrochloride) (PAH) and silica nanoparticles followed by the functionalization of a thermosensitive polymer-poly(N-isopropylacrylamide) (PNIPAAm) and perfluorosilane. A fully integrated microfluidic valve using a thermal switchable superhydrophobic/hydrophilic polymer patch has been fabricated. At 70 °C, the valve is superhydrophobic and stops the water flow (closing status) while at room temperature, the patch becomes hydrophilic, and allows the flow (opening status)