How Tethered Probes Report the Dynamics of a Polymer near the Glass Transition

Abstract

How tethered probes report dynamics of host polymers near the glass transition was investigated by changing the length of the flexible linkers and the number of tethering points via imaging rotational fluorescence correlation microscopy and compared with free probes of different sizes. The results show that tethering did not alter the temperature-dependence of polymer dynamics and the shape of the correlation decay reported by the probe; however, the rotation slowed down up to ≈1 decade when both ends of the probe were restricted with short alkyl chain linkers. Upon comparison with the bigger free probe, the mechanism of the slowdown was attributed to the restricted motion upon tethering for tethered probes compared to averaging over different regions of the dynamic heterogeneity for the bigger probe. If the size of the probe was comparable to that of the dynamic heterogeneity of the system, tethered probes accurately report dynamics relevant to glass transition, regardless of tethering conditions.

Molecular Weight Dependence of the Glass Transition Temperature (Tg)-Confinement Effect in Well-Dispersed Poly(2-vinyl pyridine)–Silica Nanocomposites: Comparison of Interfacial Layer Tg and Matrix Tg

“…Furthermore, there must be careful consideration of the choice of the tethering molecule. If the units in a tether of significant length have much more or much less intrinsic mobility than the polymer units, the T g reported by the label could be affected by the tether itself, , making the meaning of the data questionable. It may be possible to address the mobility factor, at least in part, by the use of trace levels of tethers of oligomers or low- to moderate-MW polymers that are the same species as the NC matrix. ,,, Additionally, care should be taken to avoid conditions in which the trace levels of tethered polymers can form “mushroom” structures, which can significantly affect local T g …”

Direct Observations of Segmental Dynamics at the Polymer–Substrate Interface Enabled by Localizing Fluorescent Probes with Polymer Brushes

“…CuBr 2 (>99%, extra pure) was acquired from Acros Organics. 2-Hydroxylethyl 2-bromoisobutyrate (HEBiB) and N -hexylamino- N ′-pentyl-3,4,9,10-perylenedicarboxylic diimide (PDI-NH 2 ) were synthesized as described previously. , N , N ′-dipentyl-3,4,9,10-perylenedicarboximide (pPDI, free probe) was purchased from Sigma-Aldrich. All other reagents and solvents were purchased from TCI Chemicals and Sigma-Aldrich.…”

Environmentally Sensitive Luminescence Reveals Spatial Confinement, Dynamics and Their Molecular Weight Dependence in a Polymer Glass

“…In this work, we utilized a family of thermochromic phosphorescent probes recently developed by our group for ratiometric color-based bulk T g characterization. 29 Unlike the majority of emissive probes used, for example, in the fluorescent correlation spectroscopy studies, 3,19 the CuN 4 probes (Figure 1) used in this work are designed to probe the material dynamics on the timescale of the probe photoluminescence (PL). Namely, the PL spectrum of CuN 4 and its emission color is linked to the ion pair geometry within the probe molecule.…”

“…The latter work demonstrates the importance of probe placement chemistry for interpreting the photoluminescence (PL) data. Since different parts of material can exhibit different extent dynamics, even a common choice between tethered [18][19] or freely dispersed probes defines which space in the polymer will be accessible to the probe molecules and which aspect of polymer dynamics they will ultimately describe. This touches on the principal questions one should ask when using responsive small molecules: How informative are local probe-based measurements and which local and bulk material features do they report?…”