#################################################### # Eric Mock # requesting 3 days, at minimum=3 days # beamline 33ID, Structure of Anisotropic Nanoparticles # instrument 33ID-D SRUSAXS #################################################### # top:/home/www/beamtime-requests/req00842.txt # UNICAT Member Beam Time Request #842 # created Sat Aug 20 16:47:51 CDT 2005 #################################################### apsrun: 2005-03 beamline: 33ID collaboration: Yes collaborator_Pete: ON contact: ericmock@uiuc.edu days: 3 description: STRUCTURE OF ANISOTROPIC NANOPARTICLES Anisotropic colloid particles are encountered in numerous commercial and industrial applications, including coatings, adhesives, impact modifiers, medical diagnostics and photonic crystals. Controlling the rheology and microstructure of anisotropic colloid suspensions is a major goal of the engineer and chemist. In particular we are interested in controlling the anisotropy of particle interactions to build novel microstructures to enhance macroscopic properties. In a previous set of experiments we performed side bounce ultra small angle x-ray scattering on polystyrene spheres and dumbbell shaped nanoparticles, as shown in the SEM micrograph in Figure 1. The measured intensities as a function of scattering vector, Q, are shown in Figure 2, for the two batches of particles shown in Figure 1 suspended in glycerol at a volume fraction of 0.45. Specifically, in Figure 2, the scattering patterns for the two sets of particles in Figure 1 are different and when coupled with differences in experimentally determined form factors, give differences in structure factor as seen in Figure 3. Now that we have shown differences in anisotropy of the particles in Figure 1 can be distinguished between in the particle form factors, we are working to characterize anisotropy using standard methods for calculating form factors[1]. Upon loading the samples into the USAXS sample cells, they are passed through a syringe, causing the suspensions to be sheared. For high volume fraction (phi~0.5) suspensions in water, the time necessary to reach the elastic modulus after shearing is virtually instantaneous (<10seconds). However, in the previous SBUSAXS experiments, at higher volume fractions, the glycerol suspensions appear to show an increase in ordering as they are left to sit in the sample cells after loading, as shown for the structure factors of dumbbell particles at a volume fraction of 0.463 in Figure 4, suggesting that in glycerol it is necessary to wait longer times for the suspensions to reorder after loading them. Due to time constraints, we were not able to fully look into this, thus limiting our ability to study higher volume fractions where we anticipate ordering of the particles will occur. Furthermore, the sphere (no bumps) and dumbbell (bumps of equal size) particle scattering measurements represent the limits of particle anisotropy, and thus give us a limited amount of data to develop a method for calculating form factors. Ideally, we would like to perform SBUSAXS on anisotropic nanoparticles with bump sizes between these limits. Currently we have synthesized particles with intermediate bump sizes between dumbbells and spheres, as shown in Figure 5. Therefore, we would like to study the scattering from increased volume fractions (phi~0.3-0.5) of these new bump sizes, in order to study the microstructure of dense suspensions of anisotropic nanoparticles. Likewise, we would now like examine scattering at high volume fractions (phi~0.5) after the suspensions have been loaded in the USAXS sample cells and allowed to sit unperturbed for extended periods of time (0h, 0.5h, 1h). The particles will be dispersed in glycerol at different volume fractions (phi~0.05 to 0.5 in steps of 0.1). The following are the list of experiments we plan to perform and the issues we are trying to tackle 1) Dilute solution scattering: Samples with phi~0.01: This set of runs will help us determine the scattering from a single particle and help us set the form factor. 2) Scattering from concentrated suspensions: Once the form factor is obtained, the volume fraction of the particles will be increased from dilute to concentrated (phi~0.5) and the static structure factor measured. This will allow us to study the microstructure as a function of bump size and particle volume fraction. After the structure is determined, our goal would be to analyze the scattering pattern with theoretical models: to pick an interaction potential and see if we can extract interaction potential parameters which best describe the thermodynamics of the system. 3) Scattering from ordered suspensions: Suspensions at high volume fractions (phi~0.5) will be sheared beyond the yield stress with a vortex mixer and loaded into sample cells. SBUSAXS will be performed on these samples over different periods of time, t, after they have been loaded and allowed to sit unperturbed (t~0h, 0.5h, 1h). This will allow us to see how the microstructure changes in these suspensions after ordering has been broken up by shearing. Reference 1. O. Glatter In Small Angle X-ray Scattering; O. Glatter and O. Kratky, Eds.; Academic Press: New York, 1982. STRUCTURE OF FUMED SILICA GELS Suspensions composed of fumed silica and a series of alcohols (ethanol, propanol, butanol, pentanol and hexanol) have been shown to exhibit a range of particle-particle interactions due to the surface chemistry differences of the alcohols. The strength of attraction between the particles at sufficiently high concentrations is strong enough for the liquid suspensions to form gels. A critical part of this study is investigating the different structures of the gels, as a preliminary study showed different gel structures depending on the solvent. A detailed experiment carried out on the SBUSAXS instrument would allow insights into the dependence of particle concentration and solvent on the structure of both the liquid and gels of these fumed silica suspensions. equipment_required: experiment: Structure of Anisotropic Nanoparticles foreign_nationals: hazards: Materials should not be ingested, and direct skin contact with materials should be limited. Wear proper personal protective equipment (i.e. latex or nitrile gloves, closed toe shoes, pants, safety glasses, etc.). instrument: 33ID-D SRUSAXS instrument_other: minimumdays: 3 name: Eric Mock nonmembers: submit: Submit unacceptable_dates: October 31-November 3, November 22-28 z34ID_details: #REMOTE_HOST: eric.scs.uiuc.edu #REMOTE_ADDR: 130.126.229.6 #CONTENT_LENGTH: 6421 #HTTP_REFERER: http://www.uni.aps.anl.gov/admin/unireq.html #HTTP_USER_AGENT: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)