Multilayer tubes that constrict, dilate, and curl in response to stimuli

Zarket, Brady C.; Wang, Hanchu; Subraveti, Sai Nikhil; Raghavan, Srinivasa R.

doi:10.1039/d0sm01704c

Cited by 3 publications

(2 citation statements)

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“…We then use the "inside-out polymerization" technique developed by our lab to grow a shell of NIPA gel around each of the above structures. [18][19][20] The idea behind this technique is that one of the components required for a free-radical polymerization (the initiator) is present only in the core while the others are only present in the surrounding solution. [18] Specifically, we load the cores with ammonium persulfate (APS, a thermal initiator) and then place them in a solution containing the NIPA monomer as well as other components (see Experimental Section for details).…”

Section: Synthesis Of Capsulesmentioning

confidence: 99%

“…The outer shell of the capsules is a hydrogel made of NIPA (≈500 µm thick), which we create by an inside-out polymerization technique. [18][19][20] When the capsules are heated above the LCST of NIPA, the transparent capsules spontaneously turn pearlescent (Figure 1C). The effect is reversible, with the transparent state being recovered upon cooling.…”

Section: Introductionmentioning

confidence: 99%

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Pearl‐Like Sheen in Soft Capsules: An Unusual Optical Effect that is Reversibly Induced by Temperature

Rath,

Fear,

Woehl

et al. 2023

Adv Funct Materials

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A pearl-like sheen (i.e., pearlescence) is seen in many natural materials like nacre and in some commercial paints and cosmetics. This phenomenon is attributed to the interaction of light with plate-like particles in the material. Here, for the first time, pearlescence is demonstrated in soft millimeterscale capsules that contain no plate-like particles. The capsules have a thin (~500 µm) outer shell of N-isopropylacrylamide (NIPA) hydrogel, which has a lower critical solution temperature (LCST) of 32 °C. When a transparent NIPA-shelled capsule is heated above this LCST, it turns pearlescent. The effect is reversible, with the transparent state being recovered upon cooling. This is the first example of reversible pearlescence in any solid. Specular reflectance measurements show that the pearlescence of the capsules is comparable to that of natural pearls. Pearlescence is not observed in NIPA hydrogels; it arises only in NIPA-shelled capsules, and that too only when the shell is thin. Above its LCST, the NIPA shell shrinks and gets stretched, and nanoscale NIPA-rich domains arise within this shell, which induce the pearlescence. This study sheds fresh insight into the nature of pearlescence, on how it can be tuned, and on how this property can be introduced into various soft materials.

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