Thermo-switchable pressure-sensitive adhesives with strong tunable adhesion towards substrate surfaces of different hydrophilicity

Adhesion Evolution: Designing Smart Polymeric Adhesive Systems with On-Demand Reversible Switchability

Smart polymeric switchable adhesives represent a rapidly emerging class of advanced materials, exhibiting the ability to undergo on-demand transitioning between "On" and "Off" adhesion states. By selectively tuning external stimuli triggers (including temperature, light, electricity, magnetism, and chemical agents), we can engineer these materials to undergo reversible changes in their bonding capabilities. The strategic design selection of stimuli is a pivotal factor in the design of switchable adhesive systems. This review outlines recent advancements in the field of smart switchable polymeric adhesives over the past decade with a focus on the selection of stimulus triggers. These systems are further categorized into one of four adhesion switching mechanisms upon initiation by a specific stimuli-trigger: (i) interfacial adhesion, (ii) stiffness, (iii) contact area, or (iv) suction-based switching. Evaluation of adhesion switching performance across systems is primarily made based on three key metrics: (i) maximum adhesion strength, (ii) switch ratio, and (iii) switch time. Different stimuli and mechanisms offer distinct advantages and limitations, influencing the performance characteristics and applicability of these materials across domains such as detachable biomedical devices, robotic grippers, and climbing robots. This review thus offers a perspective on the present advancements and challenges in this emerging field, along with insights into future directions.

The emulsion polymerization induced self-assembly of a thermoresponsive polymer poly(N-vinylcaprolactam)

A thermoresponsive polymer, poly(N-vinylcaprolactam) (PNVCL), was synthesized in an emulsion above its thermal transition temperature to produce particles via polymerization induced self-assembly (PISA).

Soft to tough: ordering in and tack of polymeric materials

In the present paper, adhesive properties (in terms of practical work of adhesion, W_a, and maximum stress in probe tack test) of blends of polyvinyl pyrrolidone (PVP) with polyethylene glycol (PEG-400) are studied at different level of stretching stress, applied perpendicular to the probe. The anisotropic behavior in both directions is investigated. Upon stretching, blends of 50/50 wt% PVP-PEG demonstrate little decrease in tack and little increase in maximum debonding stress. Whereas for more cohesive blends like PVP-PEG mixtures with down to 35 wt% of PEG, a significant reduction in W_a at the size of an order of a magnitude is observed. Similar behavior is measured with a commercial product from 3M with the trade name "Command". For the first time, the anisotropy of probe tack properties of two identical strips after stretching is demonstrated via a specially designed quasi-2D setup, where the external force is applied either along or transverse the long side of the quasi-2D substrate, resulting in a significant difference in the measured probe tack curves. This phenomenon has been described by the block model, developed by Yamaguchi et al. We extended the block model by introducing the stretching stress into the model. The differences are explained by the difference in kinetics of the cavity growth between the two directions.