Visualization Analysis Of Polymer Material Structure

Polymers have been used in a wide range of applications spanning from daily life,bioscience,transportation and aerospace fields.The effective and accurate characterization of the polymer material structure is the basic guarantee for the material to exert its performance and achieve efficient utilization.The characterization of polymer material structure should take the multiple components and their interactions into consideration,and thus establish an in-situ,non-destructive and multi-dimensional characterization of the polymer.The current characterizations of polymer structure are mainly based on the electron microscopy,infrared spectroscopy,and macroscopic properties of polymeric materials.However,these methods can only provide statistic results for polymers at a macroscopic scale with a limited sensitivity.In addition,characterization process causes damage to the sample,making it impossible to achieve insitu and non-destructive characterization.In this work,based on the principle of specific targeting of fluorescent molecules and laser scanning confocal microscopy technology,the non-destructive,highly sensitive and three-dimensional visualization and quantification of polymers has been realized.As a result,we have achieved the early-stage fluorescence detection towards the polymer aging,the multi-path identification for the polymer aging,and the three-dimensional evaluation of the dispersion for inorganic phase in polymeric materials.It is anticipated that the proposed method could provide theoretical basis and technical support for the design and construction of high-performance polymer materials.1.Early-Stage visualization and monitoring of polymer agingBased on the specific B-O click reaction between the fluorophorebonded boronic acid molecules and the hydroxyl groups generated by thermal aging of the polymer,an early-stage monitoring for polymer aging with high sensitivity has been achieved throughout three-dimensional imaging technique.This proposed method can identify the initial aging of polypropylene as early as 20 min for polypropylene.In contrast,no signals can be detected by conventional infrared spectroscopy even after 21-day thermal treatment.In addition,the fluorescence signal of fluorescent molecules was tracked from the three-dimension to monitor the entire process of aging from the surface to the interior of the polymers.Multidimensional dynamics simulations were performed:faster aggression in the horizontal plane(4.1 × 10-4 s-1)than in the vertical direction(2.6 × 10-9 m·s-1)for polypropylene films.This method provided a theoretical reference for revealing the mechanism details of polymer aging in threedimensional space and predicting the life for the polymers.The universality of the proposed method was further verified by monitoring the aging evolution of other polymers.2.Multi-path identification and monitoring during polymer agingMultiple aging pathways occurredd simultaneously under multiple factors in the service process of polymers.Taking polyimide as a model polymer,three types of fluorescence modified with boric acid,amino and isothiocyanate groups were used to specifically label the hydroxyl,carboxyl and amino groups in the aging process of polyimide,respectively.The excitation and emission wavelengths of each fluorescent probe were regulated to realize the effective differentiation and simultaneous imaging of polyimide aging pyrolysis and hydrolysis multi-path reactions.The reaction degrees and kinetic rate constants of the pyrolysis and hydrolysis reaction of polyimide were analyzed under different oxygen and water vapor contents.The results showed that the increase of humidity inhibited the pyrolysis reaction,accelerated the hydrolysis reaction,and intensified the entire polyimide aging.In addition,the oxygen content showed a greater impact on the pyrolysis reaction than the water vapor content had on the hydrolysis reaction.The proposed strategy can guide the long-term use of polymers,and adjust the polymer aging to a harmless direction by adjusting the contents of oxygen and water vapor.3.Three-dimensional quantitative evaluation of dispersion state for inorganic phase in polymer compositesThe inorganic phase is often used as a reinforcing filler in the organic phase to construct composite materials with excellent performances.The dispersion of the inorganic phase determines the quality and performance of the composite materials.In this section,using the layered double hydroxide(LDHs)in low-density polyethylene(LDPE)as a model,a spatial quantitative evaluation method for the particle spacing of the inorganic phase in composite materials was proposed through specific targeting of the inorganic phase and three-dimensional imaging analysis.The spatial spacing of adjacent inorganic phases was calculated by Matlab equation and fitted with Gaussian simulation.The results showed that the adjacent spatial spacing of the inorganic phase in the composite material decreased first and then increased,indicating that the dispersion state of the inorganic phase changed from "random","even" to "clustered".Furthermore,the relationship between the spatial spacing of the inorganic phase and the mechanical properties of the composite material was studied.The optimal radius for the inorganic phase was acquired in a polymeric composite material.This work provided strong support for the design of high-performance composite materials.