Rheological modifiers are added to formulations to tune rheology, enable function and drive phase changes requiring an understanding of material structure and properties. We characterize two colloidal rod systems during phase transitions using multiple particle tracking microrheology, which measures the Brownian motion of probes embedded in a sample. These systems include a colloid (monodisperse polyamide or polydisperse hydrogenated castor oil), surfactant (linear alkylbenzene sulfonate [LAS]), and nonabsorbing polymer (polyethylene oxide [PEO]) which drives gelation by depletion interactions. Phase transitions are characterized at all concentrations using time‐cure superposition. We determine that rheological evolution depends on
Dissociation energy of dynamic bonds in thermoresponsive phase‐change salogels is explored using rheology and dynamic light scattering (DLS). The salogels are formed by polyvinyl alcohol (PVA) reversibly crosslinked by hydrogen‐bonding amine‐terminated molecules in an inorganic phase‐change material—lithium nitrate trihydrate (LNH) salt—as a solvent. The crosslinker geometry (linear vs branched) has a strong effect on both the gelation temperature (
- NSF-PAR ID:
- 10459583
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Chemistry and Physics
- Volume:
- 220
- Issue:
- 22
- ISSN:
- 1022-1352
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract LAS:colloid . The critical PEO concentration required to form a gel,c c /c *, is independent ofLAS:colloid , critical relaxation exponent,n , is dependent onLAS:colloid , and both are independent of colloid polydispersity.n indicates the material structure at the phase transition. AtLAS:colloid > 16, the scaffold is a tightly associated network and atLAS:colloid = 16 a loosely associated network. -
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Purpose Both sodium
T 1triple quantum (TQ) signal andT 1relaxation pathways have a unique sensitivity to the sodium molecular environment. In this study an inversion recovery time proportional phase increment (IRTQTPPI) pulse sequence was investigated for simultaneous and reliable quantification of sodium TQ signal and bi‐exponentialT 1relaxation times.Methods The IRTQTPPI sequence combines inversion recovery TQ filtering and time proportional phase increment. The reliable and reproducible results were achieved by the pulse sequence optimized in three ways: (1) optimization of the nonlinear fit for the determination of both
T 1‐TQ signal andT 1relaxation times; (2) suppression of unwanted signals by assessment of four different phase cycles; (3) nonlinear sampling during evolution time for optimal scan time without any compromises in fit accuracy. The relaxation timesT 1andT 2and the TQ signals from IRTQTPPI and TQTPPI were compared between 9.4 and 21.1 T. The motional environment of the sodium nuclei was evaluated by calculation of correlation times and nuclear quadrupole interaction strengths.Results Reliable measurements of the
T 1‐TQ signals andT 1bi‐exponential relaxation times were demonstrated. The fit parameters for all four phase cycles were in good agreement with one another, with a negligible influence of unwanted signals. The agar samples yielded normalizedT 1‐TQ signals from 3% to 16% relative to single quantum (SQ) signals at magnetic fields of both 9.4 and 21.1 T. In comparison, the normalizedT 2‐TQ signal was in the range 15%–35%. The TQ/SQ signal ratio was decreased at 21.1 T as compared with 9.4 T for bothT 1andT 2relaxation pathways. The bi‐exponentialT 1relaxation time separation ranged from 15 to 18 ms at 9.4 T and 15 to 21 ms at 21.1 T. TheT 2relaxation time separation was larger, ranging from 28 to 35 ms at 9.4 T and 37 to 40 ms at 21.1 T.Conclusion The IRTQTPPI sequence, while providing a less intensive TQ signal than TQTPPI, allows a simultaneous and reliable quantification of both the
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Abstract The frequency distribution of solar wind protons, measured in the vicinity of Earth’s orbit, is customarily plotted in (
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