3 research outputs found
Synthesis of polymeric and macrocyclic Lewis acids: influence of backbone on degree of aggregation
No full textA simple, one-step synthesis of multinuclear Lewis acids can be driven with high selectivity towards either macrocyclic or polymeric arrays by appropriate choice of backbone framework
Optimal planning of running time improvements for mixed-use freight and passenger railway lines
No full textIn recent years, the United States has seen a renewed focus on developing improved intercity passenger railway lines and services. With the political sensitivity of public investment in rail infrastructure and accompanying shortage of state and federal funds, it is important that the most cost effective investments are selected. Many of these endeavors, including high-speed-rail projects with new, dedicated segments, involve infrastructure investments targeted at improving the speed, capacity, and reliability of existing railway lines. In most cases, these existing lines support the operation of commingled passenger and freight traffic on the same trackage. These shared trackage arrangements introduce numerous engineering and operating challenges to successfully planning and executing improvement projects. Freight, commuter, and intercity rail traffic types have inherently different performance and service characteristics that further complicate the planning of infrastructure improvements. This thesis is focused on enhancing the planning methodology of intercity passenger rail service in the United States.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-12-01The student, Brennan Caughron, accepted the attached license on 2017-12-12 at 16:54.The student, Brennan Caughron, submitted this Thesis for approval on 2017-12-12 at 17:01.This Thesis was approved for publication on 2017-12-14 at 10:06.DSpace SAF Submission Ingestion Package generated from Vireo submission #11962 on 2018-03-13 at 09:57:49Made available in DSpace on 2018-03-13T15:28:43Z (GMT). No. of bitstreams: 2
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Previous issue date: 2017-12-14Embargo set by: Seth Robbins for item 105223
Lift date: 2020-03-13T15:28:52Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 105223 on 2020-03-14T09:15:22Z
Towards reversible mechanochemically triggered strengthening, toughening and assembly of soft materials
No full textThe field of mechanochemistry is on many levels inspired by biology, where mechanical force regulates the flux of ions through channels, triggers electrochemical impulses, and activates the rearrangement of protein complexes. A key attribute of many biochemical reactions is reversibility, as this enables the machinery of cells to perform their functions many times. With the exception of color switching mechanophores, the majority of mechanochemical reactions developed in the lab are completely irreversible, thus limiting their function to a one time use. Spiropyran (SP) is a unique mechanophore that reversibly switches from a ring-closed state to a ring-open state, merocyanine (MC), in response to a variety of stimuli, including UV light, heat, and mechanical force. Herein, a strategy is proposed to reversibly crosslink polymer chains using SP’s well documented ability to bind to metal cations in its MC state.
A proof of concept is demonstrated, whereby viscous solutions containing transition metal ions and a SP functionalized polymer spontaneously switch from a viscous fluid to a viscoelastic gel in response to heat. Exposure to visible light dissociates polymer crosslinks, switching the gel back to a viscous fluid state. Rheological studies using small amplitude oscillatory shear demonstrates reversible crosslinking over several cycles. The data strongly suggest that crosslinking is due to intermolecular bridging of MC units via coordination to divalent metal ions.
A methodology is developed for incorporating metal ions into spiropyran mechanophore linked poly(dimethylsiloxane) elastomers. By removing moieties that stabilize MC, as well as incorporating additives that competitively solvate metal ions in PDMS, force-triggered MC-metal complexation is demonstrated for the first time with autonomous dissociation of the metal complexes after removal of the applied stress. Force-triggered complexation is demonstrated over many cycles without any sign of hysteresis. Though spontaneous activation is not completely inhibited it is well controlled. An inverse relationship between the thermodynamic stability of MC-metal complexes measured in solution and the ratio of mechanochemical to thermal activation in the SP-PDMS/metal ion composite is revealed. Though force-triggered crosslinking is not demonstrated in this system, these results are a significant step towards engineering systems with reversible mechanochemical functionalities that extend beyond color indication.
2D diffusion NMR is employed to gain a deeper understanding of the molecular mechanisms that result in metal-ion-mediated gelation of SP polymer solutions. A number of complexities are revealed, and a method for decoupling the effects of shape, size, solvation and charge on the relative diffusivity of MC and SP is proposed.
Implications of our findings towards the possibility of engineering SP polymers that mechanochemical strengthen and toughen are heavily emphasized. This dissertation concludes with two rational strategies for the engineer or chemist who wishes to pursue these ideas further.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-05-01The student, Eric Epstein, accepted the attached license on 2018-04-16 at 09:34.The student, Eric Epstein, submitted this Dissertation for approval on 2018-04-16 at 09:50.This Dissertation was approved for publication on 2018-04-16 at 17:10.DSpace SAF Submission Ingestion Package generated from Vireo submission #12264 on 2018-08-31 at 17:19:01Made available in DSpace on 2018-09-04T20:34:07Z (GMT). No. of bitstreams: 3
EPSTEIN-DISSERTATION-2018.pdf: 12933116 bytes, checksum: f35830496ae67b9155abb8cb68fa7f94 (MD5)
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Previous issue date: 2018-04-16Embargo set by: Seth Robbins for item 107253
Lift date: 2020-09-04T20:34:13Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107253
Lift date: 2020-09-04T20:37:00Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107253
Lift date: 2020-09-04T20:42:08Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107253 on 2020-09-05T09:15:09Z
