Open AccessIn Situ RheoNMR Correlation of Polymer Segmental Mobility with Mechanical Properties during Hydrogel Synthesis
Author(s) -
Fengler Christian,
Keller Jonas,
Ratzsch KarlFriedrich,
Wilhelm Manfred
Publication year - 2022
Publication title -
advanced science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.388
H-Index - 100
ISSN - 2198-3844
DOI - 10.1002/advs.202104231
Subject(s) - polymer , materials science , rheology , kinetics , polymer chemistry , copolymer , exponent , chemical engineering , composite material , physics , linguistics , philosophy , quantum mechanics , engineering
Understanding polymer gelation over multiple length‐scales is crucial to develop advanced materials. An experimental setup is developed that combines rheological measurements with simultaneous time‐domain 1 H NMR relaxometry (TD‐NMR) techniques, which are used to study molecular motion (<10 nm) in soft matter. This so‐called low‐field RheoNMR setup is used to study the impact of varying degrees of crosslinking ( DC ) on the gelation kinetics of acrylic acid (AAc) and N , N ′‐methylene bisacrylamide (MBA) free radical crosslinking copolymerization. A stretched exponential function describes the T 2 relaxation curves throughout the gelation process. The stretching exponent β decreases from 0.90 to 0.67 as a function of increasing DC , suggesting an increase in network heterogeneity with a broad T 2 distribution at higher DC . The inverse correlation of the elastic modulus G ′ with T 2 relaxation times reveals a pronounced molecular rigidity for higher DC at early gelation times, indicating the formation of inelastic, rigid domains such as crosslinking clusters. The authors further correlate G ′ with the polymer concentration during gelation using a T 1 filter for solvent suppression. A characteristic scaling exponent of 2.3 is found, which is in agreement with theoretical predictions of G ′ based on the confining tube model in semi‐dilute entangled polymer solutions.