DATA TITLE: Dataset PROJECT TITLE: Salt-induced coil-to-globular transition and interfacial assembly in poly(N-isopropylacrylamide)-capped gold nanoparticles system DATA ABSTRACT: The data reported here pertains to the dynamic response of aqueous solution containing poly(N-isopropylacrylamide)-capped gold nanoparticles (pNIPAM-Au NP) to the introduction of NaCl to the system. The addition of NaCl to the system increases the density of the solution and triggers the coil-to-globular transition (CGT) of the pNIPAM, prompting the liquid/liquid phase separation process and confining the polymer to a lower-density aqueous phase. As the pNIPAM-occupied aqueous phase is being excluded from the higher-density NaCl-rich bulk solution, the pNIPAM-grafted Au nanoparticles follow this liquid/liquid phase separation, assembling into globular structures where pNIPAM-grafted Au nanoparticles reside on the surface of the pNIPAM globes at the interface between NaCl-rich bulk solution and pNIPAM-containing solution and exhibiting a hexagonal packing with an inter-particle distance of ~23 nm. Driven by the minimization of hydrophobic interactions, the buoyant Au-decorated pNIPAM-filled globes escape to the air/water interface, collapse at the interface, and form hexagonal crystalline domains, depending on the NaCl concentration. At low NaCl concentrations in the bulk solution, the collapse of the globes at the air/water interface produces an interfacial two-dimensional (2D) hexagonal lattice of pNIPAM-Au nanoparticles with an inter-particle distance of 25-27 nm. The increase in NaCl concentration in the bulk of solution leads to a formation of smaller globes, escaping to and collapsing at the air/water interface, and resulting in smaller hexagonal domains. ### FILE DIRECTORY The files in this dataset contain raw scanning transmission electron microscopy (STEM) images, processes images, and ASCII files of plotted graphs. #### FILE LIST Number of files in corresponding Figures: Figure 1: Figure 1a: 1 file; Figure 1b: 1 file. Total: 2 files; Figure 2: Figure 2a: 3 files; Figure 2b: 3 files; Figure 2c: 1 file. Total: 7 files; Figure 3: Figure 3a: 2 files; Figure 3b: 1 file; Figure 3c: 2 files; Figure 3d: 1 file; Figure 3e: 2 files; Figure 3f: 2 files; Figure 3g: 2 files. Total: 12 files; Figure 4: Figure 4a: 3 files; Figure 4b: 1 file; Figure 4c: 1 file; Figure 4d: 2 files; Figure 4e: 1 file; Figure 4f: 1 file. Total: 9 files; Figure 5: Figure 5a: 1 file; Figure 5b1 2 files; FIgure 5b2: 2 files; Figure 5b3: 2 files; Figure 5b4: 2 files. Total: 9 files; Figure 6: Figure 6a: 4 files; Figure 6b: 1 file; Figure 6c: 1 file; FIgure 6d: 1 file; Figure 6e: 4 files; Figure 6f: 1 file; Figure 6g: 1 file; Figure 6h: 1 file; Figure 6i: 4 files; Figure 6j: 1 file; Figure 6k: 1 file; FIgure 6l: 1 file; Figure 6m: 4 files; Figure 6n: 1 file; Figure 6o: 1 file; Figure 6p: 1 file. Total: 28 files; Figure 7: Figure 7a: 2 files; Figure 7b: 2 files. Total: 4 files; Figure 8: 6 files. Supplementary Information Video files provide real-time acquisition of nanoparticles' globular assemblies in liquid phase. Number of files in Supplementary Materials: Supplementary video SV1: 1 file; Supplementary video SV2: 1 file; Supplementary video SV3: 1 file; Supplementary video SV4: 1 file. ## METHODS AND MATERIALS The liquid phase STEM (LP-STEM) imaging in situ was carried out using a continuous flow fluid cell holder platform (Hummingbird Scientific, Lacey, WA, USA). Silicon nitride chips were UV/O3 plasma-cleaned using ProCleanerTM (Bioforce Nanosciences, Ames, IA, USA) for 20 minutes prior to use to ensure contaminant removal. The liquid-loaded cell was formed by sandwiching two SiN coated silicon chips with a 50 × 200 µm electron-transparent 50 nm-thick SiN opening etched from the center, forming an imaging window. In our experiments, either both of the SiN windows were square windows and were lacking the 100 nm SU-8 spacers to ensure the minimal thickness of the liquid layer could be obtained during the imaging, or both SiN windows had a 100 nm SU-8 spacer, to obtain a nominal 200 nm-thick layer of liquid. ### DATA COLLECTION METHODS The STEM images were recorded using FEI Tecnai G2 F20 STEM equipped with a Tridiem Gatan image filter operating at 200 kV in high angle annular dark-field (HAADF) STEM mode. We worked in the HAADF STEM mode with condenser aperture C2 = 70 µm and a camera length of 87 mm, with the data acquisition carried out primarily at magnification range M =40,000-56,000 x and using a spot size 10. Continuous capture movies were recorded for approximately 3 minutes using a freeware screen grabber, AutoScreenRecorder (Wisdom Software) that recorded images at a rate of 8 frames per second. Video editing was performed with BigaSoft Total Video Convertor (Bigasoft 6). The synchrotron X-ray experiments were carried out on a liquid surface spectrometer at ChemMatCars (beamline ID-15) of the Advanced Photon Source (APS), Argonne National Laboratory. The incident X-ray energy was 10 keV. A typical synchrotron X-ray measurement (i.e., reflectivity and GISAXS) is performed within a time scale of approximately 30 to 60 min after varying the salt concentration in the subphase. ### DATA PROCESSING METHODS The STEM data uploaded herein are used to generate figures, linear plots, and tables associated with the data analysis in the manuscript. The Radial Distribution Function for each case was calculated using the ImageJ (https://imagej.nih.gov/ij/) macro Radial_Distribution_Function (https://imagejdocu.tudor.lu/doku.php?id=macro:radial_distribution_function) by Michael Schmid & Ajay Gopal. The position of the particles for histogram construction was obtained using a Delaunay triangulation in ImageJ. The Voronoi’s constructions were done using Scipy & Skimage packages; Matplotlib was used to plot the cells using Python 3.7.0. Reflectivity data file has "rrf" and GISAXS data file has "gisaxs" in the file names. The data files are plain text files and can be open with any text editor. Usually, the first column are X-axis values, i.e., Qz for reflectivity or Qxy for GISAXS, second column are Y-axis values, i.e., intensity or reflectivity, third column being error bars. ### SOFTWARE HAADF-STEM images have EMI/SER extensions. To open and process these images, the Reader can use the program ES Vision or TIA licensed software (ThermoFisher – FEI), or use the TIA_import_folder from the FELMI-ZFE database (https://www.felmi-zfe.at/dm_script/) to import the files into the free offline Gatan Microscopy Suite® software (GMS, Gatan Microscopy Suite® (GMS) software version 3.22.1461.0 - http://www.gatan.com/installation-instructions). Schematics and diagrams were done using CorelDRAW® 2017 version 19.1.0.414. Histograms, radial distributions and vertices/cell bar charts were plotted using Origin® 2018. ### LICENSING This work is licensed under the Creative Commons Attribution (CC-BY) 4.0 International License. For more information visit: [https://creativecommons.org/licenses/by/4.0 ](https://creativecommons.org/licenses/by/4.0)