Benzophenone Absorption and Diffusion in Poly(dimethylsiloxane) and Its Role in Graft Photo-polymerization for Surface Modification

Abstract

Following the great success of traditional microfluidic devices across many disciplines, a new class of microfluidic systems emerged in recent years, which features finely tuned, localized surface modifications within the microstructures in order to keep up with the demand for devices of ever increasing complexity (lab on chip, assay on chip, etc.). Graft photopolymerization has become a powerful tool for such localized surface modifications particularly in combination with poly(dimethylsiloxane) (PDMS) devices, as it is compatible with many functional monomers and allows for high spatial resolution. However, application within enclosed PDMS microstructures and in particular well-controlled surface-directed polymerization remains challenging. Detailed understanding of the interaction between photoinitiator, benzophenone (BP), and polymer matrix is needed. We have developed a visualization technique, which allows for observation of reacted BP in situ within the PDMS matrix. We present a detailed study on solvent-driven BP diffusion providing results essential to successful surface treatment. We also identified and investigated photoinitiator inhibition by oxygen and provide appropriate mitigation strategies.

Selective UV Reflecting Mirrors Based on Nanoparticle Multilayers

“…Excited benzophenone is known to abstract hydrogen atoms from almost all polymers, thus generating radicals, which can be produced locally at high concentration and give rise to the degradation of the matrix. [ 43 ] Hence, one of the main advantages of integrating the nanostructured inorganic multilayers herein proposed is the absence of any sort of photodegradation of the polymeric matrix without compromising the achievable degree of UV protection. Also, degradation of the polymer typically results in yellowing of the fi lm, strongly reducing its transparency after some time.…”

Selective modification for polydimethylsiloxane chip by micro-plasma

“…Chemical and physical modifications of the surface of microfluidic channel is a state-of-the-art technique to control the surface charge and hydrophilicity in the micro analysis system [1][2][3][4][5][6][7][8][9]. Micro-plasma technique has received special attention due to its application in surface modification as well as on-chip light sources and chromatography detectors [1,10].…”

“…As a result, many different methods for hydrophilization have been proposed to modify the surface of PDMS, such as rendering it hydrophilic by activating PDMS surface using oxygen plasma [9] and absorbed hydrophilic organic molecules coatings [8,12], nonetheless at the expense of its long-term stability [3]. Another conventional way of surface modification in polymer science is surface-attached polymerization, which provides chemically stable surfaces due to the covalent bonding of the polymer chains to the substrate [4][5][6]9]. Recent reports also introduce grafting of poly (acrylic acid) (PAA) on PDMS based on a liquid phase system with UV irradiation [4,5,13,14], however such method demands long operation hours, and requires strictly experimental conditions and abundant chemicals as well, some result in PDMS swelling in organic solvents, and the others poor stability and performance.…”

“…Another conventional way of surface modification in polymer science is surface-attached polymerization, which provides chemically stable surfaces due to the covalent bonding of the polymer chains to the substrate [4][5][6]9]. Recent reports also introduce grafting of poly (acrylic acid) (PAA) on PDMS based on a liquid phase system with UV irradiation [4,5,13,14], however such method demands long operation hours, and requires strictly experimental conditions and abundant chemicals as well, some result in PDMS swelling in organic solvents, and the others poor stability and performance. The micro-plasma technique with working gas He and AA presented in this work circumvents the above drawbacks, owing to its selectivity, quickness and convenience.…”

Lab-on-Chip Methodology in the Energy Industry: Wettability Patterns and Their Impact on Fluid Displacement in Oil Reservoir Models

“…Wettability patterns within the micromodels were achieved by UV-initiated graft polymerization of PAA (Schneider et al, 2010). In short, micromodels were primed with Photoinitiator Benzophenone (BP) by driving a solution of 10% (wt) BP in acetone through the device for 5 min, allowing BP to diffuse into the PDMS matrix in vicinity of the channel walls (Schneider et al, 2011). After vacuum drying for 15 min, the channels were loaded with a degassed solution of 20% (wt) acrylic acid (AA) in water and the system was exposed to UV light (365 nm) through a photomask for 3-4 min at an intensity of 30 mW cm −2 .…”