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You searched for subject:(Elastomer network). Showing records 1 – 2 of 2 total matches.

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University of Rochester

1. Meng, Yuan (1988 - ). Poly(capro-lactone) networks as actively moving polymers.

Degree: PhD, 2016, University of Rochester

Shape-memory polymers (SMPs), as a subset of actively moving polymers, form an exciting class of materials that can store and recover elastic deformation energy upon application of an external stimulus. Although engineering of SMPs nowadays has lead to robust materials that can memorize multiple temporary shapes, and can be triggered by various stimuli such as heat, light, moisture, or applied magnetic fields, further commercialization of SMPs is still constrained by the material’s incapability to store large elastic energy, as well as its inherent one-way shape-change nature. </br> This thesis develops a series of model semi-crystalline shape-memory networks that exhibit ultra-high energy storage capacity, with accurately tunable triggering temperature; by introducing a second competing network, or reconfiguring the existing network under strained state, configurational chain bias can be effectively locked-in, and give rise to two-way shape-actuators that, in the absence of an external load, elongates upon cooling and reversibly contracts upon heating. </br> We found that well-defined network architecture plays essential role on strain-induced crystallization and on the performance of cold-drawn shape-memory polymers. Model networks with uniform molecular weight between crosslinks, and specified functionality of each net-point, results in tougher, more elastic materials with a high degree of crystallinity and outstanding shape-memory properties. The thermal behavior of the model networks can be finely modified by introducing non-crystalline small molecule linkers that effectively frustrates the crystallization of the network strands. This resulted in shape-memory networks that are ultra-sensitive to heat, as deformed materials can be efficiently triggered to revert to its permanent state upon only exposure to body temperature. </br> We also coupled the same reaction adopted to create the model network with conventional free-radical polymerization to prepare a dual-cure “double network” that behaves as a real thermal “actuator”. This approach places sub-chains under different degrees of configurational bias within the network to utilize the material’s propensity to undergo stress-induced crystallization. Reconfiguration of model shape-memory networks containing photo-sensitive linkages can also be employed to program two-way actuator. Chain reshuffling of a partially reconfigurable network is initiated upon exposure to light under specific strains. Interesting photo-induced creep and stress relaxation behaviors were demonstrated and understood based on a novel transient network model we derived. </br> In summary, delicate manipulation of shape-memory network architectures addressed critical issues constraining the application of this type of functional polymer material. Strategies developed in this thesis may provide new opportunity to the field of shape-memory polymers.

Subjects/Keywords: Actively-moving polymers; Dynamic network; Elastomer network; Poly(caprolactone); Shape-memory polymers; Stimuli-responsive materials

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APA (6th Edition):

Meng, Y. (. -. ). (2016). Poly(capro-lactone) networks as actively moving polymers. (Doctoral Dissertation). University of Rochester. Retrieved from http://hdl.handle.net/1802/31452

Chicago Manual of Style (16th Edition):

Meng, Yuan (1988 - ). “Poly(capro-lactone) networks as actively moving polymers.” 2016. Doctoral Dissertation, University of Rochester. Accessed December 15, 2019. http://hdl.handle.net/1802/31452.

MLA Handbook (7th Edition):

Meng, Yuan (1988 - ). “Poly(capro-lactone) networks as actively moving polymers.” 2016. Web. 15 Dec 2019.

Vancouver:

Meng Y(-). Poly(capro-lactone) networks as actively moving polymers. [Internet] [Doctoral dissertation]. University of Rochester; 2016. [cited 2019 Dec 15]. Available from: http://hdl.handle.net/1802/31452.

Council of Science Editors:

Meng Y(-). Poly(capro-lactone) networks as actively moving polymers. [Doctoral Dissertation]. University of Rochester; 2016. Available from: http://hdl.handle.net/1802/31452


Case Western Reserve University

2. Burke, Kelly Anne. Structure-Property Relationships in Main-Chain Liquid Crystalline Networks.

Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University

Main-chain liquid crystalline networks were prepared from mesogenic dienes using two different synthetic routes. First, main-chain liquid crystalline copolymers were synthesized by polymerizing a mesogen with a nonmesogenic comonomer using acyclic diene metathesis (ADMET) chemistry. The resulting polymers form nematic phases, with composition dictating the glass transition and isotropization temperatures. Free-radical crosslinking through the unsaturated bonds in the polymer was demonstrated for a selected composition to lead to an elastomeric network. This two step process was employed to control the polymer properties before crosslinking and serves as a viable route to tailored nematic networks for applications as anisotropic adhesives. Liquid crystalline elastomers (LCEs) were prepared using a second synthetic route that employed hydrosilylation chemistry to react the mesogens with hydride-terminated poly(dimethylsiloxane) and a vinyl crosslinker. The resulting LCEs formed a smectic-C phase with transition temperatures that depend on mesogen composition. The mesogens impart two distinct active behaviors to the elastomers. The first of these is actuation, the reversible extension and contraction of the polymer when cooled and heated, respectively, through the mesogen isotropization transition. Actuation is dependent on the crosslink density of the material and can cause the samples to elongate as much as 30 % under tensile load. The second active behavior is shape memory, the ability to fix a temporary deformation and later recover the equilibrium shape by heating. The LCEs have excellent shape memory fixing and recovery ratios, both of which generally exceeded 95 %. The ability of a soft network to fix strains above room temperature is unusual and was investigated using a combination of thermal analysis, mechanical testing, and wide angle x-ray scattering, where it was found that strain is fixed by freezing the mesogens within the smectic layers. The LCE’s low modulus was exploited by reversible embossing, the localization of a temporary topography onto the LCE using shape memory. A microscale embossed topography was stable until erased by heating to recover the LCE’s flat, permanent shape. Possible applications of these LCEs include artificial muscles, smart shear-based actuators, and active substrates. Advisors/Committee Members: Mather, Patrick (Advisor).

Subjects/Keywords: Polymers; liquid crystalline; network; elastomer; main-chain; shape memory; actuation; polymer; structure-property relationship

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Burke, K. A. (2010). Structure-Property Relationships in Main-Chain Liquid Crystalline Networks. (Doctoral Dissertation). Case Western Reserve University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=case1270660447

Chicago Manual of Style (16th Edition):

Burke, Kelly Anne. “Structure-Property Relationships in Main-Chain Liquid Crystalline Networks.” 2010. Doctoral Dissertation, Case Western Reserve University. Accessed December 15, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1270660447.

MLA Handbook (7th Edition):

Burke, Kelly Anne. “Structure-Property Relationships in Main-Chain Liquid Crystalline Networks.” 2010. Web. 15 Dec 2019.

Vancouver:

Burke KA. Structure-Property Relationships in Main-Chain Liquid Crystalline Networks. [Internet] [Doctoral dissertation]. Case Western Reserve University; 2010. [cited 2019 Dec 15]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=case1270660447.

Council of Science Editors:

Burke KA. Structure-Property Relationships in Main-Chain Liquid Crystalline Networks. [Doctoral Dissertation]. Case Western Reserve University; 2010. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=case1270660447

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