a nanoparticle nebulizer for generation of aerosolized ... · aerosol particle size distribution...
TRANSCRIPT
Derek R. Oberreit1,*, David Blackford1, Gary van Schooneveld2, Seongho Jeon3
1Fluid Measurement technologies Inc., White Bear Lake, MN 551102CT Associates, Eden Prairie, MN 55455
3Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55344
AbstractDispersion of colloid nanoparticles into an aerosol first
requires nebulization of the colloid into fine droplets and
subsequent evaporation of the solvent from them. Following
solvent evaporation, droplets that did not contain a colloid
particle form particles composed of non-volatile solvent
residue. Droplets that do contain colloid particles result in
aerosolized colloid particles with a coating of non-volatile
residue. To reduce the interference by non-volatile residue
particles as well as effect on the colloid particle properties
(surface chemistry, size), it is desirable to create droplets
containing a low volume of solvent. This is especially true for
aerosolization of nanoparticles that approach the size of the
non-volatile residue particles. Nebulization is typically
accomplished using either pneumatic or electrospray methods.
While electrospray methods do provide sufficiently small
droplets (~0.3 µm), there are several limitations to the method
including poor long term stability and necessity for a
conductive solvent. Common pneumatic nebulizers create
droplet distributions with a peak diameter near 2.0 µm which
leads to a significant amount of non-volatile residue
interference in the aerosol. We present a new commercially
available pneumatic nebulizer that is designed to produce a
high number concentration of small droplets with a peak
diameter less than 0.5 µm. We compare the performance of
this nebulizer with existing aerosolization methods for a variety
of colloids. We also show additional applications of this device
for monitoring colloid concentrations in dilute systems such as
ultrapure water systems and in liquid filter efficiency testing.
Instrument Design
Introduction
Online Dilution
• Maximum non-volatile residue 1 ppm (typical of many HPLC
grade solvents)
• Less than 0.1% change in 10 nm particle diameter due to
residue
• Minimal interference by particles consisting of only NVR
Nebulizer Geometry•High purity materials of construction - minimize additional
NVR contribution
•Swept flow paths - minimize dead spaces
•Confined air-liquid mixing area – Transfer maximum gas
energy into breakup of liquid
•Ball end inertial impactor – Large droplet removal
Results
A Nanoparticle Nebulizer for Generation of Aerosolized Colloid Particles with Reduced Influence by Non-Volatile Residue
• The properties of particles in hydrosols (colloids) are
commonly measured by dispersing the colloid particles into a
gas (aerosolization)
• Primary methods for aerosolization include Nebulization
(pneumatic spraying of colloid) and Electrospray
(electrohydrodynamic spraying)
• Electrospray is not suited for all colloids and are anecdotally
unstable over long periods
• Nebulization using traditional devices typically creates
droplets on the order of 2 µm
• Non-volatile residue (NVR) in the solvent creates a particle
which is proportional to the diameter of the droplet
• As colloid particle sizes approach the size of the residue
particles, the resulting aerosol particles no longer represent
the particles in it
• Goal: Design a pneumatic nebulizer which reduces the effect
of non-volatile residue on the resulting aerosol
Nebulized Droplet Distribution•Significant reduction of the peak droplet diameter
•Leads to reduced non-volatile residue interference
• Online dilution of sample will lower the peak diameter of non-
volatile residue particles• Minimizes contamination from sample vials
• Useful to lower NVR resulting from stabilizers with minimal
coagulation due to short diluted residence time.
DispersionParticles in
SuspensionEvaporation
DispersionParticles in
SuspensionEvaporation Diameter
Peak Shift
Traditional
nebulizer
1 ppm non-volatile residue With 20 nm particle
25% Increase
in size
<0.1%
Increase in
size
2 nm
20 nm
Model 7788
nebulizer
Plumbing and Electrical•Evaporator and nebulizer temperature control
•Monitor Sample pressure and temperature
•Sample taken from pressurized stream or injected directly
Liquid Filter Testing• Nanoparticle nebulizer output particle concentration measured using a condensation particle counter with a 50% detection
efficiency at 10nm
• Downstream cumulative (>10 nm) colloid particle concentration
measured throughout filter challenge
LiquiTrak® Model 7788 Nanoparticle Nebulizer
•Manufactured by Fluid
•Measurement Technologies Inc.LiquiTrak®
Liquid Nanoparticle Sizer (LNS)•Model 7788
•Model 7780 LNS Dilution Module
•Scanning Mobility Particle SizerPatent US 8,272,253, US 8,573,034, US 7,852,465
Aerosolization of colloid particles•Aerosol size distribution measured with a Scanning Mobility
Particle Sizer (LNS system)
•Good agreement shown between aerosol particle size
distribution and colloid size distribution
Fractional coverage (Monolayers)
0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200
Re
ten
tio
n (
%)
0
20
40
60
80
100
Silica
PSL
Gold
30 nm Rated Water Filter Challenged with 2E8 #/ml ( 6ppm) 30nm Particles
8 10 12 14 16 18
Fra
cti
on
(%)
0.0
0.1
0.2
0.3
0.4
0.5
10 12 14 16 18 200.0
0.1
0.2
0.3
Colloidal particle size distribution
10nm AuNp 15nm AuNpMean 11.71 nm
Mode 12.00 nm
Mean 15.76 nm
Mode 15.00 nm
Size(diameter, nm)
6 7 8 9 20 30 40 5010
dN
/dlo
gD
p
0
2000
4000
6000
8000
10000
12000
Size(diameter, nm)
6 7 8 9 20 30 40 50 60100
2000
4000
6000
8000
10000
12000
1400010nm AuNp
Dilution ratio
1000
15nm AuNp
Dilution ratio
500
Mode 13.1 nm Mode 16.8 nm
Aerosol particle size distribution
Primary particle size (nm, log scale)
Primary particle size (nm, linear scale)
Normalized 10:1(mass ratio) TiO2/calgon size dsitributions with different dilution ratios
Size(nm, log scale)
6 7 8 15 30 40 50 60 70 80 15010 100
Y/Y
ma
x
0.0
0.2
0.4
0.6
0.8
1.0
1.2
500
1000
2000
5000
10000