Opto-chemo-mechanical transduction in photoresponsive gels elicits switchable self-trapped beams with remote interactions

Abstract

Next-generation photonics envisions circuitry-free, rapidly reconfigurable systems powered by solitonic beams of self-trapped light and their particlelike interactions. Progress, however, has been limited by the need for reversibly responsive materials that host such nonlinear optical waves. We find that repeatedly switchable self-trapped visible laser beams, which exhibit strong pairwise interactions, can be generated in a photoresponsive hydrogel. Through comprehensive experiments and simulations, we show that the unique nonlinear conditions arise when photoisomerization of spiropyran substituents in pH-responsive poly(acrylamide-co-acrylic acid) hydrogel transduces optical energy into mechanical deformation of the 3D cross-linked hydrogel matrix. A Gaussian beam self-traps when localized isomerization-induced contraction of the hydrogel and expulsion of water generates a transient waveguide, which entraps the optical field and suppresses divergence. The waveguide is erased and reformed within seconds when the optical field is sequentially removed and reintroduced, allowing the self-trapped beam to be rapidly and repeatedly switched on and off at remarkably low powers in the milliwatt regime. Furthermore, this opto-chemo-mechanical transduction of energy mediated by the 3D cross-linked hydrogel network facilitates pairwise interactions between self-trapped beams both in the short range where there is significant overlap of their optical fields, and even in the long range––over separation distances of up to 10 times the beam width––where such overlap is negligible.

Light-Directed Organization of Polymer Materials from Photoreactive Formulations

“…Another approach is through the growth of vertically aligned microfiber optic arrays which can be overlaid on a solar cell, which also increases energy conversion . One other application has used the filaments and their interactions for computing and data storage, with the polymer medium itself able to perform the computations and store information. , …”

From Appendage to Crosslinker – Unusual Swelling Behavior in Spiropyran-Modified Hydrogels

“…2) in the context of our efforts to design optically active, self-regulated hydrogels. 44,45 To this end, spiropyran variants 1 and 2 were synthesized (SI Sections 1 and 2) and co-polymerized into methylenebisacrylamide-crosslinked polyacrylamide hydrogels (SI Section 3, Tables S3.1-S3.3, verification of attachment by FTIR in SI Section 5.1). The spiropyran-free, control hydrogel, p(AAm-co-AA) polymerized at a 1:1 AAm:AA molar ratio and crosslinked with 1.1 mol% methylenebisacrylamide (BIS), swells in aqueous media with a swelling ratio (SR) increasing from ~2 to ~11 as pH increases from pH 5.5 to 7.5, due to the accumulation of negative charges on the polymer backbone resulting from the deprotonation of carboxylic acid moieties (pKa ~4.7, Fig.…”

“…Finally, we note that the presence of spiropyran aggregates may have significant effects on non-linear optical phenomena such as beam-trapping, which are under investigation in our laboratory. 44,45…”

“…Stimuli-responsive swelling/contraction for hydrogels with appended spiropyrans relies on changes in charge and polarity between the positively charged MCH + , zwitterionic (overall neutral) MC, and neutral SP spiropyran isomers. 19,20,44 We therefore set out to elucidate the isomer distributions for both spiropyran variants at different pH values in the gel to understand whether the difference in swelling could be explained by differences in isomer distribution (and thus changes in osmotic counterion pressure) alone. To that end, UV-vis spectroscopy was used to identify spiropyran isomer signatures in buffered spiropyran solutions and in hydrogels (SI section 5.3) to understand how solution pH, covalent attachment, and hydrogel volume affect spiropyran isomer equilibria.…”

Liquid Cybernetic Systems: The Fourth‐Order Cybernetics

“…One of the most remarkable results achieved so far is the observation of the interaction between laser beams and a hydrogel medium: the laser beam is able to modify the distribution of molecules in the hydrogel on the one hand, and to receive a focusing effect on the other hand, whereas normally the beam is broadened while travelling. [ 60 ] The same hydrogel is able, furthermore, to act as distributed interaction facilitator, as two laser beams “feel” each other even when their optical fields are not overlapped. Such interaction is tunable, which represents the fundamental ingredient to engineer practical computational paradigms ( Figure ).…”