復(fù)合材料教案

1、Teaching TopicChapter 6 Polymer nanocomposites Lecturing hours 180 minTeaching Objectives1. Know the general features of polymer nanocomposites;2. Know the preparation methods of polymer nanocomposites;3. Know the characterization of polymer nanocomposites.Teaching Emphases1. The feature of polymer

2、nanocomposite.2. The preparation of polymer nanocomposite.Teaching Difficult PointsThe characterization of nanocomposites.Teaching MethodsLecturing + PPT + discussion + interactionTime ArrangementTeaching content45 min6.1 Introduction 1. definitionWhen inorganic phases in organic/inorganic composite

3、s become nanosized, they are called nanocomposites.Organic/inorganic nanocomposites are generally organic polymer composites with inorganic nanoscale building blocks. 2. Advantages inorganic material organic polymer 3. Defining feature of polymer nanocomposites the small size of the fillers leads to

4、 a dramatic increase in interfacial area as compared with traditional composites. This interfacial area creates a significant volume fraction of interfacial polymer with properties different from the bulk polymer even at low loadings.4. Inorganic nanoscale building blocks Nanotubes;Layered silicates

5、 (montmorillonite, saponite),Nanoparticles of metals (Au, Ag), Metal oxides (TiO2, Al2O3),Semiconductors (PbS, CdS),Others.5. Polymer/Silica SiO2 is viewed as being very important.Polymer/silica composites are the most commonly reported in the literature. They have been employed in a variety of appl

6、ications.6. Discuss: what is nanocomposite?6.2 Preparation of nanocomposite Organic or inorganic polymerization generally becomes necessary if at least one of the starting moieties is a precursor. Blending is generally just mixing of the silica nanoparticles into the polymer; a sol-gel process can b

7、e done in situ in the presence of a preformed organic polymer or simultaneously during the polymerization of the monomer(s); the method of in situ polymerization involves the dispersion of nanosilica in the monomer(s) first and then polymerization is carried out 45 min6.2.1 Blending Melt ble

8、nding Melt blending is most commonly used because of its efficiency, operability, and environmental containment. Matrices: Polymers and polymer blends Level : less than 3 vol %many advantages:being simple, low cost, easy to control and broadly applicable. . Solution Blending Solution blending

9、 is a liquid-state powder processing method that brings about a good molecular level of mixing and is widely used in material preparation and processing. Some of the limitations of melt mixing can be overcome if both the polymer and the nanoparticles are dissolved or dispersed in solution but at a c

10、ost depending on the solvent and its recovery. The location for solution blending is not limited to a solution can include a latex or a suspension. and then compression molding is also applied. Other Blending Methods To overcome these problems is :to process the polymer in the solid state, wh

11、ich avoids the thermal and solvent problems encountered with traditional technologies while providing almost infinite design flexibility and processing simplicity. 6.2. 2 Sol-Gel Process Sol-gel reaction is a method to prepare ceramic precursors and inorganic glasses at relatively low temperatures.

12、The major advantage of the process is that mild conditions, such as relatively low temperature and pressure, are used in this type of processing of ceramics. the sol-gel process can be viewed as a two-step network forming process:the first step being the hydrolysis of a metal alkoxide the second con

13、sisting of a polycondensation reaction. The properties of the resulting nanocomposites influenced by particle sizes and interaction between the dispersed and continuous phases.According to the nature of interfacial interaction, hybrid materials can be divided into two distinct classes, 6.2.3 In Situ

14、 Polymerization . General PolymerizationThere are several advantages of using the in situ polymerization method. These include:ease of handling, the speed of the process, and better performance of the final products. The process of in situ polymerization involves three continuous steps: The m

15、ost important factors that affect the properties of composites are:the dispersion and the adhesion at the polymer and filler interfaces.Inorganic particles may disperse homogeneously in the polymer matrices when they are premodified by a coupling agent. Photopolymerization It is a process whe

16、re UV light induces the polymer formation allowing a fast transformation of the liquid monomer into the solid film with tailored physicochemical and mechanical properties. In the process, radical or cationic species are generated by the interaction of the UV light with a suitable photoinitiator, whi

17、ch induce the curing reaction of reactive monomers and oligomers. Surface-Initiated Polymerization A key feature in the construction of nanocomposite systems is the development of specific interactions at the interface of the organic and inorganic components, because the interface plays a do

18、minant role in the preparation and properties of nanocomposites. Therefore, the development of grafting strategies so as to tailor the surface properties of mineral substrates is of great current interest. 6.3 Colloidal Nanocomposites These materials represent a new category of nanocomposites, which

19、 can exhibit remarkable properties (mechanical, electrical, optical, chemical, rheological, etc.) by an appropriate combination and structuration of the organic and inorganic components inside the nanoparticles.Colloidal polymer/silica nanocomposites Principally colloidal polymer/silica nanocomposit

20、es can be divided into systems with a polymer core and a silica shell or vice versa. Various methods have been developed for their preparation, and they typically involve:the sol-gel process (resulting in coating of polymer colloids with silica), in situ heterophase polymerization (usually resulting

21、 in polymer encapsulation of silica nanoparticles), self-assembly technique. 6.4 Incompatibility of polymers and minerals in order to circumvent the inherent incompatibility of polymers and minerals, the synthetic procedures of nanocomposites commonly require significant affinity between silica surf

22、aces and polymers, whichever preparative method was used. Controlling the morphology 45 min6.5 Characterization and Properties The properties of the nanocomposites strongly depend on their composition, the size of the particles, interfacial interaction, etc. The interfacial interaction between polym

23、er and silica strongly affects the mechanical, thermal, and other properties of the nanocomposites. The internal surfaces (interfaces) are critical in determining the properties of nano-filled materials since silica nanoparticles have high surface area-to-volume ratio, particularly when the size dec

24、reases below 100 nm.This high surface area-to-volume ratio means that for the same particle loading, nanocomposites will have a much greater interfacial area than microcomposites. 6.5.1 Chemical Structure The chemical structure of polymer/silica nanocomposites is generally identified by FTIR and sol

25、id-state 29Si NMR spectra. FTIR spectrometry is widely used to prove the formation of nanocomposites especially for those prepared by the sol-gel reaction, in which process a silica network can be formed. 29Si solid-state NMR gives further information on the structure of silica and the degree of Si-

26、OH condensation reaction. 6.5.2 Microstructure and Morphology Crystallization behaviors of the silica nanoparticle-filled composites are usually studied by DSC. TEM is a microscopy technique whereby a beam of electrons is transmitted through an ultrathin specimen and carries information about the in

27、ner structure of the specimen. SEM a type of electron microscope that creates images by the electrons emitted when the primary electrons coming from the source strike the surface and are in elastically scattered by atoms in the sample.AFM is an effective tool to characterize nanocomposites by provid

28、ing the morphological information. 6.5.3. Mechanical Properties . Tensile, Impact, and Flexural Properties. Hardness . Fracture Toughness . Friction and Wear Properties 6.5.4. Thermal Properties Thermal properties are the properties of materials that change with temperatu

29、re.They are studied by thermal analysis techniques, which include DSC, TGA, DTA, TMA, DMA/DMTA, dielectric thermal analysis, etc. TGA/DTA and DSC are the two most widely used methods to determine the thermal properties of polymer nanocomposites. DSC can be efficiently used to determine the thermal t

30、ransition behavior of polymer/silica nanocomposites. the CTE, which is the criterion for the dimensional stability of materials, can be measured with TMA. Dielectric thermal analysis is also useful to understand the viscoelastic behavior of the nanocomposites. 6.5.5. Flame-Retardant Properties A fir

31、e retardant is used to make materials harder to ignite by slowing decomposition and increasing the ignition temperature. It functions by a variety of methods such as absorbing energy away from the fire or preventing oxygen from reaching the fuel. Polymer nanocomposites for flame retardant applicatio

32、ns are attractive, and the nanoscale silica particle is a new type of nanoparticle for flame-retardant nanocomposites. 6.5.6. Optical Properties The most important optical properties of a material are its transparency and refractive index. Transparency is the physical property of allowing the transm

33、ission of light through a material. Introduction of silica inorganic nanoparticles even at low contents into transparent polymers often leads to opaque nanocomposites due to light scattering caused by the nanoparticles. 40 min6.5.7 Gas Transport Properties Gas transport properties include solubility

34、, diffusivity, permeability, and permselectivity.6.5.8. Rheological Properties Rheology is the study of the deformation and flow of matter under the influence of an applied stress. The measurement of rheological properties is helpful to predict the physical properties polymer nanocomposites during a

35、nd after processing. 6.5.9. Electrical Properties Electrical properties of polymers include several electrical characteristics that are commonly associated with dielectric properties and conductivity properties. Electrical properties of nanofilled polymers are expected to be different when the fillers get to the nanoscale for several reasons. 6.5.10. Other Characterization Techniques The particle size distributions of the colloidal nanocomposites can be assessed using two techniques: d