properties. [9,10] While fluorescence has been used extensively to characterize bulk properties of polymers, including glass transition temperature (T g ) [11][12][13] and polymerization conversion, [13] it is particularly well-suited to study polymers at the nanoscale. This is largely due to the fact that fluorescence techniques enable sensitive and location-specific measurements with high resolution.In this review, we focus on the use of both steady-state and transient fluorescence techniques to characterize physical properties of polymers over nanoscale dimensions. This length scale can refer to film thickness in single-component polymer films, interparticle spacing in nanocomposites, domain spacing in phaseseparated block copolymers, and distance from the polymer-polymer interface in multicomponent immiscible blends. Several geometries characterized via fluorescence are shown in Figure 1. Prior to delving into specific contributions, the basic principles and techniques of fluorescence are presented as well as a brief introduction to the behavior of confined polymers. We then present recent advances in fluorescence techniques for polymer physical characterization under confinement with regards to the glass transition temperature, physical aging, mobility and diffusion, and mechanical response. Through this examination of the literature, we illustrate the unique ability of fluorescence to characterize polymers in confined and complex geometries, providing insights into the influences of interfaces and nanostructure on material properties through sensitive, location-specific measurements. We conclude with a view toward future areas of research in which fluorescence has the potential to be impactful. Introduction to FluorescenceWhen a molecule absorbs energy via light, an electron is excited to a higher energy state, returning to the ground state through either radiative or nonradiative deactivation. This electronic excitation and return to the ground state is a combination of three photophysical processes: absorption, luminescence, and nonradiative decay. [33] Fluorescence is a luminescent process in which the excited-state electron returns to the ground state by emitting a photon, i.e., light. As shown in a simplified Jablonski Polymer CharacterizationCharacterization of polymers at the nanometer-length scale has become increasingly important with the growth and expansion of nanotechnology. Due to limitations of sensitivity and specificity that persist with traditional materials characterization techniques, there is a growing need to develop new tools to measure the properties of confined polymer systems. Within the past 20 years, fluorescence characterization techniques have emerged to address this challenge. This review focuses on the employment of fluorescence techniques such as temperature-and time-dependent steady-state intensity, fluorescence recovery after photobleaching, and nonradiative energy transfer to study polymer behavior at the nanoscale. Properties discussed include glass transition temperatur...

In an effort to incorporate increasingly higher levels of functionality into soft nanoparticles, heterogeneously structured particles stand out as a simple means to enhance functionality by tailoring only particle architecture. Various means exist for the fabrication of particles with specific structural configurations; however, the tunability of particle morphology is still a challenging and often laborious task, especially in self-assembled systems where a single equilibrium configuration dominates. Improved strategies for multipatch particle assembly are therefore needed to allow for the tailoring of particle structure via a single, continuous assembly route. One means of accomplishing this is through kinetic trapping of particle morphologies along the path to the final equilibrium configuration in precipitation-induced, phase-separating polymer blends. Here, we demonstrate this capability by using rapid nanoprecipitation to control the overall size, composition, and patch distribution of soft colloids. In particular, we illustrate that polymer feed concentration, blend ratio, and polymer molecular weight can all serve as functional handles with which to consistently alter particle patch distributions in a self-assembling homopolymer system without redesigning the starting materials. We furthermore delineate the role of polymer vitrification in the determination of particle structure.