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The focus of the present paper is the rheological study of poly(D,L-lactic-acid) (PDLLA) towards a modeling of their healing properties during 3D direct pellet printing extrusion (DPPE). The viscoelastic properties of PDLLA and the filament temperature during deposition are first characterized. The influence of DPPE processing conditions is investigated in terms of temperature, time, and printing speed. For this, we propose a modeling of the process-induced interphase thickness between two deposited layers considering the non-isothermal polymer relaxation and accounting for the contribution of entanglement rate through the Convective constraint release model. Hence, taking into account the induced chain orientation and mobility coming from filament deposition, this model quantifies the degree of healing between 3D-printed layers. Eventually, the proposed model is validated by comparing the theoretically calculated degree of healing with experimental tensile properties and lap shear results. [ABSTRACT FROM AUTHOR]

Abstract: A method for active noise cancelation that uses an optically transparent membrane is described. The membrane consists of a prestretched hydrophobic elastomer, attached to a rigid frame and sandwiched between two hydrogels swollen with an aqueous solution of salt. The elastomer functions as a dielectric, and the hydrogel functions as an ionic conductor. When the two hydrogels are subjected to a sinusoidal voltage, the membrane generates sound. A linear model for the reflection, transmission, and generation of sound by the membrane in an impedance tube is presented and validated. Active noise cancelation is demonstrated using the linear model and feedforward control. Compared to passive sound absorption, the sound transmission loss across the membrane is improved with active control from an average value of 7 dB to an average value of 16 dB. The transparent membrane may be used to cancel noises through a window, while maintaining its transparency. [ABSTRACT FROM AUTHOR]

New applications of hydrogels draw growing attention to the development of tough hydrogels. Most tough hydrogels are designed through incorporating large energy dissipation from breaking sacrificial bonds. However, these hydrogels still fracture under prolonged cyclic loads with the presence of even small flaws. This paper presents a principle of flaw‐insensitive hydrogels under both static and cyclic loads. The design aligns the polymer chains in a hydrogel at the molecular level to deflect a crack. To demonstrate this principle, a hydrogel of polyacrylamide and polyvinyl alcohol is prepared with aligned crystalline domains. When the hydrogel is stretched in the direction of alignment, an initial flaw deflects, propagates along the loading direction, peels off the material, and leaves the hydrogel flawless again. The hydrogel is insensitive to pre‐existing flaws, even under more than ten thousand loading cycles. The critical degree of anisotropy to achieve crack deflection is quantified by experiments and fracture mechanics. The principle can be generalized to other hydrogel systems. [ABSTRACT FROM AUTHOR]