Block copolymer micelle formation was studied by a combination of fluorescent probe and quasi-elastic light scattering (QELS) techniques. The polymers, polystyrene-poly(ethy1ene oxide) diblock and triblock copolymers, with M. values ranging from 8500 to 29 000, form spherical micelles in water over the entire concentration range over which QELS signals can be detected. Pyrene (Py) in water (6 X IO-' M) partitions between the aqueous and micellar phases, accompanied by three changes in the pyrene spectroscopy. There is a red shift in the excitation spectrum, a change in the vibrational fine structure of Py fluorescence (11113 decreases from 1.9 to 1.2), and an increase in the fluorescence decay time (from 200 to ca. 350 ns) accompanying transfer of Py from an aqueous to a hydrophobic micellar environment. From these data, critical micelle concentrations (range: 1-5 mg/L) and partition coefficients (3 x lo6) can be calculated.Block copolymers of polystyrene (PSI and poly(ethy1ene oxide) (PEO) form spherical micelles in water when the length of soluble PEO is significantly longer than that of the insoluble PS portion of the m o l e~u l e .~~~ This behavior is common to both PS-PEO diblock and PEO-PS-PEO triblock copolymers. In analogy with low molecular weight surfactants, one defines the onset of intermolecular association as the critical micelle concentration (cmc), and the theories of polymer mi~ellization~ predict that in the presence of micelles, the concentration of free, unassociated block copolymers is close in magnitude to that of the cmc.There are relatively few studies devoted to determination of cmc values for block copolymer micelles. Scattering techniques, which are very powerful for determining the size and shape of the micelles, are able to detect the onset of association only if the cmc occurs in a concentration region where these techniques are sensitive. For block copolymers in water, this is often not the case. For the examples considered here, the cmc values lie well below the smallest concentrations detectable by either Rayleigh or quasi-elastic light scattering (QELS).Fluorescence techniques have been used with great success in the study of low molecular weight surfactant micelles.6 They are useful not only for cmc determination but also for measuring the aggregation number of the micelles. By comparison, aqueous block copolymer systems have received scant attention7 Several years ago Ikema et al. reported very interesting results using l-anilinonaphthalene fluorescence to probe micelle formation in a water-soluble block copolymer.'* Because the change in the fluorescence signal they observed occurred in a concentration region too small for a corresponding change to be observed by light scattering, the authors chose not to interpret this signal as an indication of the onset of polymer association. This absence of clear-cut results seems to have discouraged others from applying these methods. It isonlyrecently that there has been an outburst 0024-9297/91/2224-1033$02.50/0 of activity in the stu...

Poly(butyl methacrylate) (PBMA) latex labeled with either phenanthrene or anthracene derivatives in low concentrations (1 or 2 mol %) was prepared by semicontinuous emulsion polymerization.The latex film formation process was studied by analysis of the nonradiative energy transfer from phenanthrene (donor) to anthracene (acceptor). Initially, when the latex film dries, there is little energy transfer, indicating that the particles conserve their individual identity. With increasing time at temperatures above the glass transition temperature of PBMA, the extent of energy transfer increases. This is a clear indication that interdiffusion of polymer chains across particle boundaries occurs. The diffusion coefficient D of the polymer was evaluated by using models based upon Pick's second law. In each sample, the magnitude of D decreases with time. Initial D values increase with increasing temperature, taking values between 1 X 10"14 to 1 X 10"18 cm2/s, yielding an apparent activation energy of 38 kcal/mol. The diffusion data also fit well to the Williams-Landel-Ferry equation. The results demonstrate the great potential of fluorescence techniques in the study of polymer diffusion processes during latex film formation.

The diffusion of polymer molecules across an interface is an important topic in polymer physics. Measuring this diffusion process requires a labeling experiment so that the mixing of otherwise identical molecules can be followed. Here we examine the use of nonradiative energy transfer to follow the interdiffusion of polymer molecules during the annealing of latex films. Those films are prepared from a mixture of phenanthrene (Phe, the donor)- and anthracene(An, the acceptor)-labeled poly(butyl methacrylate) (PBMA) latex particles. We examine in some detail the kinetics of direct energy transfer (DET) at an interface and the evolution of the DET kinetics as the components mix. Time resolved and steady state measurement approaches are compared, and the former is employed to examine molecular diffusion in a series PBMA latex films. Various diffusion models are considered. Diffusion coefficients are calculated by treating the data in terms of a Fickian spherical diffusion model. A film from one set of samples is similar in molecular weight to that studied by small angle neutron scattering (SANS) [K. Hahn, G. Ley, H. Schuller, and R. Oberthur, Colloid Polym. Sci. 264, 1029 (1986)]. Diffusion coefficients calculated from both sets of experiments using similar Fickian diffusion models are very similar in magnitude.

The rapid development of light detection and ranging (LiDAR) techniques is advancing ecological and forest research. During the last decade, numerous single tree segmentation techniques have been developed using airborne LiDAR data. However, accurate crown segmentation using terrestrial or mobile LiDAR data, which is an essential prerequisite for extracting branch level forest characteristics, is still challenging mainly because of the difficulties posed by tree crown intersection and irregular crown shape. In the current work, we developed a comparative shortest-path algorithm (CSP) for segmenting tree crowns scanned using terrestrial (T)-LiDAR and mobile LiDAR. The algorithm consists of two steps, namely trunk detection and subsequent crown segmentation, with the latter inspired by the well-proved metabolic ecology theory and the ecological fact that vascular plants tend to minimize the transferring distance to the root. We tested the algorithm on mobile-LiDAR-scanned roadside trees and T-LiDAR-scanned broadleaved and coniferous forests in China. Point-level quantitative assessments of the segmentation results showed that for mobile-LiDAR-scanned roadside trees, all the points were classified to their corresponding trees correctly, and for T-LiDAR-scanned broadleaved and coniferous forests, kappa coefficients ranging from 0.83 to 0.93 were obtained. We believe that our algorithm will make a contribution to solving the problem of crown segmentation in T-LiDAR scanned-forests, and might be of interest to researchers in LiDAR data processing and to forest ecologists. In addition, our research highlights the advantages of using ecological theories as guidelines for processing LiDAR data.