Stimuli-responsive transformation in carbon nanotube/expanding microsphere–polymer composites

Abstract

Our work introduces a class of stimuli-responsive expanding polymer composites with ability to unidirectionally transform physical dimensions, elastic modulus, density, and electrical resistance. Carbon nanotubes and core-shell acrylic microspheres were dispersed in polydimethylsiloxane, resulting in composites that exhibit a binary set of material properties. Upon thermal or infrared stimuli, liquid cores encapsulated within the microspheres vaporize, expanding the surrounding shells and stretching the matrix. Microsphere expansion results in visible dimensional changes, regions of reduced polymeric chain mobility, nanotube tensioning, and overall elastic to plastic-like transformation of the composite. Here we show composite transformations including macroscopic volume expansion (>500%), density reduction (>80%), and elastic modulus increase (>675%). Additionally, conductive nanotubes allow for remote expansion monitoring and exhibit distinct loading-dependent electrical responses. With ability to pattern regions of tailorable expansion, strength, and electrical resistance into a single polymer skin, these composites present opportunities as structural and electrical building blocks in smart systems.

Stimulus-active polymer actuators for next-generation microfluidic devices

“…For other stimulus domains, specifically tailored concepts for in-line control must be developed. One possible strategy that has already been demonstrated is the dispersion of electrically conductive particles in the polymer matrix and measurement of the changes in electrical conductivity or resistance that accompany the deformation of the polymer actuator [49]. The use of composites A conspicuous feature of recently presented novel and innovative concepts for polymer-based actuators is the use of composites in various ways-in the form of layered or foamed structures, as homogeneous mixtures of two or even more constituents, and as suspensions of polymers with small particles that induce an additional functionality.…”

“…11). Again, upon thermal or infrared stimulation, the material undergoes visible dimensional changes, but additionally the conductive nanotubes in the polymer matrix exhibit a load-sensitive electrical response and thus allow remote expansion monitoring [49]. Further, pure CNT networks within the silicone elastomer have been used to fabricate electrothermal actuators with a visible maximal strain of 4.4 % at an electric power density 0.03 W/mm -3 [50].…”

“…Cantilever-like actuators have typically been realized either in direct contact with a c SEM of loose, expanded microspheres (average diameter of 17.8 ± 3.8 lm). From [49], Ó2013 IOP Publishing Ltd. Reproduced with permission liquid electrolyte or as a multilayer structure with organic electrolytes, and reviews of such concepts are given in [56,57]. Another interesting application in microfluidics was described in [58], where conductive composites and fluids with giant electrorheological properties were combined to realize a microfluidic logic switch and inverter in a single microfluidic chip.…”

CHAPTER 7. Interfaces in Composite Materials

“…Inclusion of microfluidic channels, that can expand on demand, within the flexible matrix extends the application of these composites for live analysis of captured rare cells, e.g., circulating tumor cells. 105 Composites with anti-bacterial properties have also been produced by plasma grafting of anti-bacterial nanoparticles onto a polymer matrix. 106 Various smart, anti-cariogenic, pH-responsive, dental nanocomposites have been prepared by incorporating different calcium phosphate fillers (e.g., amorphous calcium phosphate, nano-tetracalcium phosphate, mixture of mono-calcium phosphate monohydrate and b-tricalcium phosphate).…”

Rapid design and implementation of semi-automated research-grade test systems

“…Therefore, we present a basic set of steps for rapid development and implementation of a reliable, repeatable, and accurate test systems in a minimal timeframe. The method presented herein has been successfully demonstrated in numerous test systems developed by the author [1][2][3][4][5][6][7]. Furthermore, obtaining research funding is becoming increasingly competitive [8]; therefore, innovation is essential for researchers to both first discover new material phenomena, as well as modify existing material properties to exceed previous best-known values.…”